So that great novel it is not going to happen unless you have written a fair share of good short stories in your twenties.
That huge programming project again unless you've mastered your chosen language and the domain space, you are just going to be dissapointed.
There are many things that make me happy, but there are no grand plans left.
Trivial example: I took 6 months of daily Duolingo practice in German to keep up with my daughter. I was making some progress but it was slower than hers. It became apparent that unless I dedicated myself fully to study I would not be able to read Grimm's fairy tales much less Kant.
It is as Stephenson wrote: "Until a man is twenty-five, he still thinks, every so often, that under the right circumstances he could be the baddest motherfucker in the world. If I moved to a martial-arts monastery in China and studied real hard for ten years. if my family was wiped out by Colombian drug dealers and I swore myself to revenge. If I got a fatal disease, had one year to live, devoted it to wiping out street crime. If I just dropped out and devoted my life to being bad."
It may mean sacrificing other things in life to accomplish, but if that's what makes you happy, the sacrifice shouldn't be a big deal. If making that sacrifice is too great, then it isn't what REALLY makes you happy, is it?
Now the "do whatever I want" thing works for a short period of time, but at some point you get to the end of the doing everything you want, and realize if you shit on everyone around you, you still aren't happy. And if you don't come to that realization... well... the rest of society is going to figure out how to deal with you and you probably aren't going to like that. not doing bad is just as much about self-preservation as anything else for those people who don't have a moral compass.