You will tend to overfit to your first users.

Underfit products are generalizable, but don't do anything.

Overfit products only work for the precise thing they're optimized to.

The ideal is the goldilocks zone of perfectly fit.

Even better is when that goldilocks fit is built out of building blocks, allowing the same code to have goldilocks fit to someone else with only minimal reconfiguration.

The pre-assembled Lego set ideal.