How Not to be Limited by Your Assumptions

how to identify wrong assumptions
Photo by Vanessa Garcia from Pexels

Wrong assumptions lead to bad decisions, poor planning and unwanted outcomes

Assumptions are often necessary for decision-making, but we need to avoid wrong suppositions if we want to make the right choices. We can get things wrong by applying assumptions in inappropriate circumstances, basing expectations on bad data, or making assumptions based on wrong thinking.

I have experienced the results of decisons made on poor assumptions and, in the process, learnt a lot about how best to avoid them.

A truly immersive cinema experience

I was in my room, watching the Lord of the Rings (The Return of the King) on my laptop. I had my earphones in and, despite the small screen, I was gripped. It was the battle of Minas Tirith, and the city was surrounded by an evil horde of orcs with their siege engines. As the army attacked the city and the rocks flew from the catapults, pounding the citadel I could almost feel the walls shaking. Another huge stone soared through the air to strike. Boom! My chair wobbled. 

The sound on my laptop was good but I had definitely felt something. I took out my earphones and listened. The was a crashing sound, this time from outside my room, not from my computer. 

Bother I thought, we are under attack. 

This was a fair assumption as I was in a military base just outside Basra in 2004. It just turned out that, in a weird bit of synchronicity, that the local militants had decided to attack our base with rockets, just when I was enjoying a bit of downtime and watching a movie. Very inconsiderate of them I thought. 

So, I put on my helmet and body armour and – doing my best to exude calm – walked out of my room into the chaos outside, then headed to the operations room. All the while I was thinking, “we expected to be welcomed; we were coming to help after all.”  How wrong we were!

Assumptions, decision-making and planning

There is a phrase about presuppositions, famous in military circles:

“Assumptions are the mother of all f***-ups”


This is not entirely true, but it does highlight the fact that bad assumptions can have disastrous effects. In the Army, when judgements often have life or death implications, making a wrong assumption could be fatal, as I nearly found out while working as a bomb disposal officer in Africa. And again now, in Iraq, it was turning out that the decisions and planning were based on some very poor assumptions. As a result, the situation was a mess.

What is an assumption and are all assumptions bad?

An assumption is something we accept to be true, even if we are lacking all the evidence. But assumptions are not necessarily bad. We sometimes need to make assumptions in decision-making as we cannot have absolutely all the information we want or need when making a choice. 

For example, when I go to buy a flat white from a coffee shop, then I assume that the barista knows how to make one. I will probably look for information to back up that assumption such as, whether they list a flat white on the menu. To reduce the risk of the assumption I might also employ a heuristic (a decision-making hack), such as going to a shop I know and trust, to reduce the risk of getting a bad coffee. In this case, the assumption and the heuristic are sound. However, if I employed that same assumption in the wrong place, for example, a Turkish coffee house in Istanbul, then I might be disappointed when it comes to a flat white. Not only that, but I would also be missing out on some excellent Turkish coffee due to my bias for flat whites!

So, we can make assumptions in our thinking but first, we need to separate out what is a fact and what is an assumption. Once we identified an assumption then we must be sure it is a reasonable one, particularly if we take an assumption we often make and then apply it to a new context. 

Assumptions based on inaccurate information

Some assumptions are not just applied to the wrong situation, they are based on corrupt data in the first place. We can compound the problem by then taking this inaccurate or limited information and then processing it poorly, due to cognitive bias. Going back to my earlier story, this was certainly the case with the war in Iraq. 

Donald Rumsfeld, the American politician, famously said:

“Because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns—the ones we don’t know we don’t know. And if one looks throughout the history of our country and other free countries, it is the latter category that tends to be the difficult ones.”

There is a lot of wisdom there; although it is unfortunate that Rumsfeld himself did not pay enough attention to his own advice. It turns out, what were thought to be knowns were not knowns at all. They were a mixture of assumptions and wishful thinking.

In 2003, a bunch of bad assumptions, built on poor information, resulted in the US-led coalition intervening in Iraq and deposing Saddam Hussein. The intelligence cited in the ‘dodgy dossier’ has long been challenged. The evidence was based not just on bad information but was also warped by cognitive bias.

Bad assumptions just breed further wrong assumptions

And these assumptions and biases played out at every level. I deployed to Iraq fully believing that we wouldunearth weapons of mass destruction at any moment. For me the logic was simple. Saddam Hussein had used chemical weapons before, in the Iran-Iraq war and even against his own people. Therefore, when I heard that he still had weapons of mass destruction that made perfect sense. Apart from the fact he didn’t. We were suffering from narrative bias, amongst other things.

One of the populations who suffered from these chemical weapons and other persecution were the Shia tribes in Southern Iraq. So, we assumed a welcome after Saddam was removed and we went to rebuild Southern Iraq. This was positivity bias at the very least, but also a massive lack of true understanding. It did not take many months, or many rocket attacks and roadside bombs, to realise quite how wrong our assumptions were. 

So, we must not apply our assumptions to the wrong situation. Nor do we make assumptions on bad data. And that means not being selective in the information one chooses to consider. To reduce the negative effects of cognitive bias we must employ a range of information sources and a diversity of viewpoints.

Negative assumptions based on bad thinking

The other trap we can fall into with assumptions is bad thinking. By that I mean we can have wrong assumptions that are embedded, often unconsciously, in our minds. These beliefs often come from bad experiences or negative things that have been said to us in our past. If someone calls you “stupid” then you can start to believe it. We can start to believe these are facts when they are, at best, just subjective ideas.

Negative assumptions are often tied up with our feelings of self-worth. For example, you could be attracted to someone but afraid to ask them out on a date. You might be thinking “I am not good enough for them” or “they are out of my league.” These were certainly my thoughts when I met one particularly beautiful girl back in college. When I spoke about her with my friends, even they thought I was trying to bat above my average (thanks guys!) Fortunately, I overcame this wrong thinking (and bad advice) and nearly 20 years later I am still happily married to that wonderful woman.

“The most tenacious block to new ideas is limiting assumptions.” 

Nancy Kline

We all have hang-ups and insecurities that clog our neural pathways. The author and coach Nancy Kline calls these blockages in our minds limiting assumptions. Limiting assumptions stop us from thinking and acting properly. In my experience, a large part of coaching is listening out for such internal defeater-beliefs and asking incisive questions to help clear them away. And if you don’t have a coach to talk through your decision then ask yourself, what assumptions am I making that are just subjective thoughts? 

We all must make a philosophical choice about what we choose to believe. Take a good look at what you think is true; examine it and test it before you make a decision – particularly an important one – based on that assumption.

The four steps to testing assumptions

As we have seen, assumptions are often necessary for decision-making but wrong assumptions can lead to poor choices and bad outcomes.

So, if we want to avoid poor assumptions follow these four steps:

  • First, separate out assumption from fact. 
  • Second, only use an assumption in the appropriate context.
  • Third, don’t make an assumption based on bad information or selected through bias.
  • Fourthly, examine your beliefs to ensure they are not just limiting assumptions based on wrong thinking. 

If we make these checks then we are much more likely to be able to make a good decision. You can start with a choice you have to make today. Have a think through the four steps. What assumptions are you making and are they rational?

And remember, as decision-making guru Darren Matthew observes,

“Your important decisions will work better with fewer assumptions.”

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