Developer
I want to invent something cool.
Dropbox, Github
Frustrating is that mostly no one cares about anything new. New things are confusing and difficult and require learning and time.
Rewarding is breaking through the barrier above with an offering that power users and early adopters "get" and actually use/love/support!
Giving up
There are a lot of hats to wear when creating a company, so adapt quickly and make it happen.
Marketing is an interesting exercise in understanding human behavior.
Be like a cockroach and survive whatever comes your way.