Like, who has the authority to say “thou shalt not try things that might fail”? As long as you’re not conning anybody out of resources, your failure doesn’t pick anybody else’s pocket.
What about altruistic reasons for asking? If my friend is planning to quit their job and become a famous musician I would probably attempt strongly to dissuade them, even if it wouldn’t directly affect me.
If however I thought they were likely to succeed (e.g. have made money selling music on bandcamp and performing, in talks with a record company, etc.) I probably wouldn’t dissuade them.