Missed opportunities? Pretty much every day of my life until I was about 26 years old, sadly. I could write about 100 of them here, easily, but I would have to dig deep into chapters of my life that I had buried!
I was raised as a super prude by my paranoid parents (to the point that I saw my sister's boobs down her pj top and my mom grounded us both for a week--my sister for not wearing a bra to bed, and me for looking).
I missed out on playing strip poker with 6 hot girls of my best friend (female). I was the only guy. I got scared and left the house.
I missed out on a FFM threesome with two women who were lesbian but wanted to prove that they weren't.
Missed out on plenty FFM threesomes in college because I was super scared.
All kinds of things. Then I met my wife who HAD done all that stuff plus a million more things and was done with it all by the time we met. I wanted to do the opposite and START it all. So instead I just live through her stories.