Kind of well known but I think bears endless repetition.

There will come a time when someone in a very large organization will take an interest in your product. You're going to feel very validated because now you can tell friends, family, investors, potential customers that X is using/piloting your product. They may or may not give you money, but it will certainly be less than your time is worth. They will definitely take a very long time to make any kind of decisive move. It is very likely that they will destroy your focus and never actually become a real customer. The longer you engage with them, the more you will want to make something come out of it and the worse the impact will be.