If someone asks you for something, it should bring something to both of you. That does not only mean money, but could also be a new experience, new contacts, and above all, good feelings.
You know that you can't do it
Optimism is a good character trait, but not when you know that you can't handle something. Stick to a realistic idea about what you can handle and how quickly you can do it.
-kk-
Article source Inc.com - a U.S. magazine and web focused on starting businesses