Research has suggested that more people regret things they didn't do than the things they did, even if things didn’t go the way they’d hoped. After all, you can only fix things that you’ve done not things that you’ve failed to do.
This research focused on three things:
Our actual selves
The traits and abilities we think we possess; basically, who we think we are.
Our ought selves
The traits and abilities we think we should possess; basically, who we think we should be (think responsibilities and obligations).
Our ideal selves
The traits, abilities, and accomplishments we would like to possess; basically, our goals and hopes and dreams.
It found that most people (72%) felt regret related to their ideal self as opposed to their ought self (28%). When asked to name their single biggest life regret, 76% of participants cited an action not taken that would have helped them realise their ideal self.
In this way, most people regret thinking they didn't reach their full potential. Ought-related regrets are easier to solve - go to the gym more, make sure you prepare in advance for meetings, save money rather than treat yourself on your credit card - however ideal-related regrets are more complicated, and are more likely to remain unresolved.
In this way, we most regret not becoming the person we feel we could have become if we only had tried. For many people this involves their career, whether it's changing careers entirely, taking a step back and spending more time with family, setting up a business or leaving the rat race for a new kind of life. And because that is one mistake you can never go back and fix, now is your chance to try.