The whole idea stems from the fact that the fall of man started due to a LIE: that we could be like God. God set a truth, and we didnt like it; we altered reality (or tried to anyway) be accepting a lie. Since than, it has been a battle: Truth versus Lie.
Whats a lie anyway? i would use my own definition: trying to alter reality to what we want
Uh, kinda like Thanos (no endgame spoilers btw):
He did not like the reality, that people struggle and starve and what have you got. So he swore to change it. In his case, he litteraly changed reality,(cuz he got the gauntlet) but in OUR case its a good analogy. The Avengers stop him (pretend they are the truth).
As you can tell, im christian and im proud