To succeed we must commit. We must invest ourselves in the course of action that we are following. This is not to say all our eggs should be in one basket but rather there should be at least some eggs in the basket and the leftover eggs should still be in the carton not some other basket. If we are trying to accomplish one thing in five ways at the same time we can do none of them well.
The skills used to do different projects will be similar, the energy needed to produce results will be similar but its a problem when your efforts are spread out across different areas. Better, faster, stronger results are to be had by putting all effort into one project.
This is not to say that we should only work one project at a time just one project per endeavor.