“The illusion that we understand the past fosters overconfidence in our ability to predict the future.” - Daniel Kahneman
People who have achieved success in their lives often have no accurate idea what exactly made them successful.
They may speculate that it was because of their skills, or the decisions that they have made in the past, but they don't actually have proof of any of these things being the actual cause.
Universally, people struggle to account for luck in their achievements and don't have the ability to see how much more successful they could have been if they hadn't made certain decisions.
Some of the most brilliant people have never achieved success, and some of the most unskilled have had remarkable success.
Because of this misunderstanding of success in the past a huge risk opens up when basing future decisions on these flawed assumptions.
Academics call it 'hindsight bias' - everyone else calls it being cocksure.