I would add :

Not treating it like a business
You cannot just party all the time and expect to pay the bills!

Expecting a new business to make money right away so they quit real jobs or don't look for real work
At least 6 months to break even point, usually more. At least a year until you can survive without outside income

Thinking that their idea is going to turn the porn world on its ear.
Honey, you may be cute but you ain't that bright. You ain't got nothin' that someone else hasn't already tried