People, you know this is one of the Vito`s famous phrases. But I need you to explain me something. I know what "but" is, I mean, I know the meaning. When you say "yes, but I don`t like it" for example.
My question is... why does "but" appear in the phrase?
Can`t I just say "every man has one destiny"?
What is the difference with "every man has BUT one destiny"?

Well, it's like every men only has one destiny.

You can also say 'Every man has no destiny's but one destiny'

The but tends to imply that there's no way to avoid ones destiny, it can't be changed.

"Every man has one destiny."
Well yea but it can be what you choose it to be.

"Every man has but one destiny."
Stop kidding yourself. You aren't a lawyer you're a mafioso. No matter what you try and do there's no way to change this pre determined fate. Michael wanted nothing to do with the family business, but his nature wouldn't allow it (for example).

Thank you Don Jimbob