It robs joy, and drains focus for the NOW. This builds a negativity mindset, one where all compliments are distrusted, all opportunities are dreaded. In this world, the only efforts wth making are ones with guaranteed outcomes. Which are few and weak.
The ultimate regret: failing to finish a dream. Seek to prevent that. Keep your eyes forward; find dreams and embrace them. Then steel yourself to fight, fumble and stagger your way forward. It's helps to focus forward, towards the top of the hill we're climbing. Efficiency often is inelegant. Crossing the finishline is ultimately what matters, whether perfectly coiffed or dripping sweat.
Updated: I found this graphic that sums this up well. Enjoy!