Psychological experiments reveal that people's biggest regrets follow predictable patterns across cultures: education, career, love, and parenting. The "time machine question" - what would you change if you could go back? - consistently surfaces these four themes. Interestingly, regrets of action (bad choices made) peak in young adulthood, while regrets of inaction (missed opportunities) dominate middle age. Stanford researchers developed "regret therapy" where patients write letters from their future selves, gaining perspective on current decisions. The healthiest approach isn't eliminating regret - that's impossible - but developing "regret resilience" through self-compassion and corrective actions when possible. Our regrets map the distance between who we were and who we've become.