How did Columbus and his crew not give up after a while with no sight of land?

https://en.wikipedia.org/wiki/Celestial_navigation

That should answer all your navigation questions.

Regarding crew morale, I haven't studied Columbus since maybe HS, but I do recall the voyage was a fairly close thing. His calculations severely underestimated the size of the Earth, so he was sailing for much longer than he expected to be. I'm not sure if he had to put down any attempted mutinies, but it wouldn't surprise me.

how did Columbus stumble upon America without getting lost?

He was lost, he was sailing for the Orient. He grossly misunderestimated the circumference of the world.

misundereatimated

... So he over estimated it?

Latitude was somewhat easy to determine since antiquity and the equipment to find it was common on most ships as was current speed in the ocean. Most cargo ships sailing out of sight of shore would try to aim laterally for the city in question then sail near the coast to get to where they needed to go.

Longitude took until the late 18th century to find as it required an accurate clock set to a known meridian. Before then, it was a guess based on approximate recorded speed.

Columbus was an idiot who miscalculated the circumference of the Earth, but crews at the time commonly sailed out of sight of shore.

The story of that clock's evolution is cool. Unfortunately I can't remember where I saw it.

Edit
This one is close but a but a bit dry.

https://m.youtube.com/watch?v=i0VFLs7vbLc

It is a Bushism meaning to mistakenly underestimate something.

I think the deal was that hé got lucky. He calculated a much smaller earth but it worked out because he thought hé was going to sail to "India". Nobody knew there was a whole:ass continent in between. Which is why it's called the West Indies and we still have "Indians" in the American West

TIL

https://en.wikipedia.org/wiki/Bushism