I don't really find this to be effective advice, for everyone at least. I could believe that some people can have multiple major projects going on at once, but I think for many, trying to split attention between projects will hurt both. That's been the case for me at least.<p>I'm not talking about some consulting gig or school paper or something. These things you can juggle. But if you are pouring your heart into a start-up, that leaves little time to build a side project.<p>I agree with the sentiment that one should think through good ideas and tinker with them though, particularly before changing course. I have what I think is a great business idea most weeks, and they do tend to already be done, harder than I think to build, or not as valuable as I had originally thought, ginned up on coffee some excited morning or beer some fun night.