Purpose of spell?

I know this might sound judgmental or ignorant, and that’s not my intention. But I can’t help wondering what’s the point of casting spells if there’s no guaranteed result and you’re just told to “trust the universe”? I thought the purpose was to help manifest what you desire, but if the universe decides not to grant certain things, then what’s the point? I realize how this might come across, but I’m genuinely curious… I thought witchcraft was supposed to empower you, not lead to a dead end when your spells don’t work. I’m not speaking from personal experience, but from posts here where people ask why their spells fail, and the answer is often that ”it was not meant for you”, but isn’t it ultimately up to us to determine what is meant for us? As you understand I'm uneducated about this, so I'm just trying to learn..