Stayed in Canada too long.

It had always been in the back of my mind to move to the US for work but I never did due to not being confident enough.

I realized in my mid-30's that I was approaching a "now or never" scenario and finally made the move to the Bay Area. I really wish I had done it right away at the start of my career rather than spending time at small companies working on small projects.

I know it's better late than never but I know I would have been so much further along in my career by now had I followed my instincts.