The Parable Of The Three Astronauts

Three entrepreneurs want to build three rocket ships. They each design a capsule and the rockets, attach engines, put on their suits and climb aboard. They strap themselves into the seat.

The first entrepreneur does the countdown and flips the switches. He feels a slight rumbling. "Is this working?" he says. He feels another rumble. "Oh my god! It's working!" 
He starts shaking with the ship, bouncing around. The ship is ship is shaking so hard that he's almost broken free of his straps, he needs to press more buttons, he yells into the radio "Houston! It's working, we're flying!". 

The second entrepreneur climbs into her rocket, and presses the ignition button. She feels the rumbling, waits a second, and aborts. She climbs down.

The third entrepreneur straps themselves in, presses the ignition button, and feels the same slight rumbling. Then, immediately, they feel like a donkey kicked them in the guts. 7G's of force push them into their seat and it's hard to even move their hands to press the radio button. The solid booster kicks in and they now it feels like an elephant kicked them in the guts. Can't even radio earth, let alone move an arm. The earth is spiraling out beneath them, vomit lines the inside of the helmet.

The third entrepreneur will be fine. They are in outer space somewhere. The second entrepreneur will probably be fine too —she can try again or she can get a nice job somewhere. The first entrepreneur? His ship never moved. It stopped rumbling months ago, but for all we know he's still bouncing around the inside of his capsule, talking to Houston and mashing buttons.

So my advice to you is: don't fall in love with your own product. Don't get high off your own supply. Product-market fit is unmistakeable. If you even think you don't have it, then you don't.