I don't think the author was saying not to put effort into anything, and certainly wasn't saying not to take advantage of opportunities. I think it just has more to do with your mindset. Are you doing things simply because you want to be "great", or is it because you actually enjoy what you do? If you're never going to be content until you become the next Steve Jobs, and that lucky break just never comes along, then what kind of life is that? You could spend a whole lifetime as a solid, successful person, and
still be miserable. What a waste.
I would also argue that, yes, Steve Jobs and Bill Gates just did things they were obsessively passionate about, and the fact that their passions turned out to line up well with what was marketable and under-exploited at the time was accidental luck. And working hard was their choice, but what about the many others who were inevitably working just as hard? They might've had a similar passion, but they weren't lucky enough to have the skills, timing, and luck that Bill Gates and Steve Jobs had. I would hope they don't spend their lives feeling inadequate because of that.
C.S. Lewis said, "Even in literature and art, no man who bothers about originality will ever be original: whereas if you simply try to tell the truth (without caring twopence how often it has been told before) you will, nine times out of ten, become original without ever having noticed it." Replace originality with greatness, and telling the truth with following your passion.