Some of the replies seem to revolve more around regret. I used to regret a lot but I ended up in a happy place so I regret less these days.
I do try to learn from my mistakes as:
"The unexamined life is not worth living"
--Socrates
So I do reflect a lot.
As for seriousness before transition started, yes, I was way too serious and it was stressing me out. I did have a try at being more light hearted but ran into a problem of not being taken seriously (is that ironic, ironic or Alanis Morissette, ironic?) or being accused of not being devoted to the task at hand.
Now, I go with the flow a lot more. I still care and can still be serious, but I don't treat everything like everything has dire consequences if things go awry. So I think I'm finding a balance. Call it Informed Optimism?