Its not. Start on your own, keep the equity, and in 6 months you can hire the same person for just a salary and only 1 or 2%
Had the wrong cofounder on the third one though, and I can't stress enough how important having the right cofounder is after that experience. It wasn't all bad, and could have been much worse, but enough to know how important a choice that is.
I'd break it down into 3 things to look for in a cofounder: proof that they're hard-working, that they have complementary skills, and that you really gel with each other. Kinda gotta feel the last one out, but the others should show up in their past work and their work ethic.