I'll bet you think you know what I'm going to say already.
Consider this.
How do you decide/measure which pie tastes best at the County Fair? You taste it and go with your personal preference. Simple. If enough of you agree; you have a Blue Ribbon awarded and that particular pie is deemed "best".
Agreement=Best
That won't work on matters which aren't mere opinion or preference, however.
If a billion people decided to vote on repealing the law of gravity we'd not find ourselves floating in mid air.
That is the chief difference between matters of taste and opinion and matters of fact.
Then there are the groups who decide, "Yes, we shall repeal the laws of gravity" and then simply declare that it is accomplished! Certain gurus do this. They teach their students that you can levitate with proper meditation procedures. You can see the photo of them levitating in the books they write. Of course, it is a brief moment in time when the shutter snaps as they BOUNCE in the air. The photo freezes the "levitation" as "proof" and the students are convinced it is possible as well as documented.
Until and unless we carefully distinguish between what we willfully decide is true and separate that decision and belief from contradictory realities we are only playing a game with ourselves. If you join a group that will automatically reinforce the same beliefs you have; a happy group delusion ensues and they call it RELIGION.
Now, there is a third thing I might mention. Reinforcement of enjoyment.
If you see a comedy alone in a theatre it isn't nearly as funny as when there is a vast audience screaming hysterically.
That reinforcement modifies the level on which our enjoyment can be accessed and experienced. You might say all those positive "votes" make what is happening absolutely "true" where True=Funny.
But, we all know that.
There is a scale from black to white in all things. Where we choose to stand pretty much creates our SENSE of reality. It doesn't create reality. No. Just OUR particular sense of it.
Science attempts to define the entire scale from black to white and assign numbers to the placement of value.
Agree or not; doesn't matter. What is IS. What is not; is NOT. Opinions don't count.
So then, belief is a most useful tool for maximizing any situation. We can modify how we feel about something simply by deciding to. That is terrific!
You look at your boyfriend and decide his crooked nose is "cute". You look at yourself in the mirror and decide you look pretty good for your age. Much more practical than breaking up with old crooked nose or joining a gym or paying for a makeover. Choice is a lovely option.