You touch on a couple of points here — I’ll try to unpack and comment :)

• Regarding the right people to take feedback from: founders to get advice from all sorts of players. Some are qualified to comment, others might be deemed less so. For me, it’s more a question of a) having open ears to learning from as many sources as you can (you don’t know what you don’t know until the time comes), and b) making sure that those you pitch to actually consider the opportunity properly before they dismiss/invest in you.
• Not understanding the opportunity or looking for a sure thing: depending on what stage you invest at, there’s a balance that needs to be struck between appetite for risk and upside potential. The fundraising process is matchmaking, really. Unfortunately, it’s hard to find that right date on the first go, so there’s some trial, error, and hypothesis reformulation that naturally has to occur. People can have opinions on a subject that ultimately are proven wrong with hindsight. That’s why I think it’s key to log the thought process that underlies an opinion at T0. When Tn comes, you’ll be able to make the pragmatic comparison and learn from it.