Bad decisions are made for many reasons, these are some common errors;
Sunk cost bias
Taking sunk costs, time, money, or other resources which have already been spent and can’t be recovered, into decision making.
Egocentric bias
Putting yourself in another person’s shoes is harder than it seems
Confirmation bias
Allowing your existing opinions, to influence the way that you interpret information – simply confirming what you already know without due consideration.
Overconfidence
That’s easy…
Endowment effect
People tend to place a higher value on things that they own relative to objects they do not.
Biased by recent events
Recent and memorable events have a greater relative influence, so much so, that we think that these type of events are more likely to happen than they actually are.
Conformity
If everybody else think so…
Illusion of control
People know gambling doesn’t pay on average, yet gladly gamble their own money. In the same way, people who say they will hit an aggressive deadline even though there are many factors out of their control.
Generalizing personalities
Most people tend to over-emphasize personality-based explanations for the actions of others.
Competitive relative comparisons
‘Happiness’ is often seen as a function of what you have relative to other people.
