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1. No, it will not necessarily happen. You can focus on one thing and still fail. See the story about the guy who dropped everything to try and be a professional golfer.That's a matter of ambition/risk. That guy will still be a very good golfer if he focuses on that. It's just that he many not be good enough to make a career of it. So yes he will look foolish but in the end, he will still be better than the rest.
If we scale back the risk levels, then this is probably true. For instance, focus on a particular field of software where there is a decent demand and you will very likely be able to live off of it.
Focus on being the founder of a successful company in a space that can only tolerate at most a handful of players (that's pretty much any business, once you properly define it) is a LOT harder and sheer willpower is not the only thing required to be successful.