because i don't see it

There's not so much a line between the two as instead a layer of marble rye between a slab of white and a slab of wheat.

Confident would be knowing you can do something

Like if you trained, studied, or prepared a lot
You know your ability and you're pretty sure of yourself

Whereas arrogance is just thinking you're the shit at everything
Even if you are unqualified to do so

Having a good understanding of your own self doesn't always mean you have to use that understanding with too much pride.

I believe that is what separates the two.

Confident would be knowing you can do something

Like if you trained, studied, or prepared a lot
You know your ability and you're pretty sure of yourself

Whereas arrogance is just thinking you're the shit at everything
Even if you are unqualified to do so

This

Confidence: I'm good at this/I hold this opinion.
Arrogance: I'm better than everyone at this and I need them to know it/My opinion is objectively correct and I need everyone to know it.

Confidence is knowing you can do something, with knowledge or experience to base upon.

Arrogance is "knowing" you can do something, with no knowledge or experience prior.

The line between those is kinda obvious, although life isn't as clear cut that way. Betting you I could beat you at a game of pool would be arrogant, seeing as I know nothing of your skill and I myself aren't great. Confidence would be betting you I could beat you, knowing that I'm a world champion in the sport and that I know you aren't into pool.

Confidence is expertly orchestrating mouth to mouth CPR on man with facial herpes.

Arrogance is going down on the janitor's wife without a face mask