I would ruminate less and act more, instead of driving myself into anxiety and depression through overthinking how to 'optimize' life.

I would focus on the guitar, start the band, and give it my all, in stead of talking myself into something safe and sensible and selling the guitar.

I would stick with electrical engineering in college, instead of abandoning it halfway through because I thought I 'wasn't smart enough'.

I would stop worrying about trying to control how others see and think of me, instead of driving myself into anxiety, depression, and obesity through trying to convince others I was something I wasn't.