No.

My personal Sunset Rule might be handy.

If I can't make a sale by sunset, I figure my idea is worthless + I get a new idea.

You can scale this also... so if I can't make several $1000s of sales for a few hours work, then I get a new idea also.

Tip: If you make sales for $0 investment, you can never go upside down + your idea will scale forever.