People believe in Bitcoin because there is something in it that they saw and want to. For example, investors believe in Bitcoin and invest in it because they saw it's potential to grow in price while others who believe in its technology, invest in it to support it.
Then it can LITERALLY apply to anything...
it does apply to everything else too!
but the difference is that when something also has some utilities to offer it gains a solid growth instead of a fake and unstable one. and bitcoin has that. it offers a lot of things from being a currency to use worldwide without border to being a store of value to safely put your money without anyone being able to touch it or probably even know about it.
this has nothing to do with "believing" in anything, it is about seeing the reality and wanting to use it.