Delusional?

What separates a "dreamer" from someone who is delusional?

I don't know the exact definition of someone who is a "dreamer"
It's usually a word for someone with an ambition, a dream, something they just want to do.
They usually see a way when others don't.

If they see things others don't, wouldn't that make them delusional...
make them crazy, or stupid or something...
If someone is trying to do something and everyone else doesn't see the purpose, the reason
they don't see the shinning outcome at the end, to them that person looks absolutely ridiculous.

There isn't much of a difference.
The only thing that separates a "dreamer" from the delusional is success.
If they can capture what they saw and all the others around them didn't....