There is a phenomenon where people playing in a casino, after winning, set aside their initial amount of money they brought with them, and call everything above that the "house's money" and then play with it without worry, taking greater risks and lacking fear of loss. This violates the principle of money's fungibility and only mentally puts the player in a state of safety. The winnings are already theirs, just like the money they brought with them.

Novice entrepreneurs often fall into this mental trap when they are unwilling to make an initial investment or make it extremely low, wanting to invest and grow the business only from its profits. The same thing happens when receiving investments: many reject or postpone this opportunity. And since there is no money for business development, what does everyone do in this situation? That's right! They make the product themselves, without selling it, without investing in marketing, without developing the product at the necessary speed.

What to do and how to fight this? First of all, as soon as you feel that instead of doing the founder's work, you start taking on the role of the one who makes the product, ask yourself: "Why do I believe so little in my product that I do everything myself instead of hiring professionals and seeking money for it? What numbers and experiments do I need so that I or investors believe in the startup?"

P.S. - I myself am a victim of this mistake and constantly try to overcome it, and it's not easy.