- I spread your idea because it makes me feel generous.
- …because there’s a financial benefit directly to me (Amazon affiliates, mlm).
- …because it’s funny and laughing alone is no fun.
- …because I can use the idea to introduce people to one another, and making a match is both fun in the short run and community-building.
- …because your service works better if all my friends use it (email, Facebook).
Like them? There are more down on his blog