So let's say that you're playing through The Adventures of Lolo and you accidentally make a puzzle unsolvable

There's no time limit, so what do you do? Reset your NES and use the last password that you got to start over?

Well, yeah, you could do that, but there's a better way.

If you press the Select button, Lolo will do... something, and lose a life, resetting the level

You can do this as many times as you want... until you run out of lives, but since continues are unlimited, it's not a huge deal.

Just be aware that you're going to be applying this liberally as you progress through the game, it gets kind of tough.