We all have made decisions that in hindsight would have been better not having made or definitely should have been modified to get a better result than we achieved. Sometimes, the consequences can be minor and we kind of shrug it off. However, when it is major it is a different story.
The results we expected to have happen seemed so straight forward at the time of making the decision. We didn't foresee the result we got; but, in hindsight we don't see how we could have missed it. So we feel we screwed up; big time.
What's wrong with this picture?
No one has a crystal ball. Our predictions are based either on our direct experiences or on knowing the results generated by someone else and our determination of the relationships between causes and effects. If we don't have perfect knowledge or the correct understanding then we get unexpected results.
All we have done is once more proved that the future is always a prediction. Our best guess. The phrase comes to mind:
If hindsight were foresight then we would make no mistakes.
It is our choice whether we beat ourselves up for mistakes or learn from them.