How do you determine the value of an asset that does not generate cash flow?

Just got curious because people trade assets that don't generate cash flow all the time like art, gold, bitcoin, pokemon cards, or even startups. Do they just buy it hoping to find somebody else who's willing pay higher price? or is it because the chart tells you how the price will change?

Even for Tesla shareholders, what convinces you that Tesla should be valued at around $1.5T right now? Would you still buy it if Tesla is at $15T today and there's still demand in the market like how GameStop did? Just by considering how much money they make at the current level, their current valuation doesn't make sense to me although I might have a better idea if I did some math to guess which business will make how much money in 5 years or 10 years.

Open to any thought you have on this topic or method you use.