It's nice when a friend serves as the devil's advocate. It also motivates you to make a list of possible cons and come up with solutions. But it's also important to watch out for toxic friends... Some are happy to bring you down every chance they get because they are either unhappy with their lives, hateful towards others, or jealous that you dared to dream big. I have been fortunate to NOT have friends like that most of my life, but I know people who have suffered from a lack of support.

I also believe it's totally normal to fail. Failure is a part of life and nearly every successful project has 10 failed ones behind it. However, a good friend would try to prevent you from spending a ton of money on objectively awful ideas.