But that doesn't answer the question at all. The question becomes, how do you stay motivated for those 3 years?
The answer, for me and people I know, is that you have to break it down into small pieces (month-sized, then week-sized, then day-sized) and find happiness in the progress. In the small daily wins.
If you think you'll only be happy once you succeed (3+ years later) you'll never make it. It's trite but it's true, that you've got to find happiness in the journey, not just the destination.
Because if you don't, then you'll absolutely give up and fall back to the things that do give you instant happiness today, whether that's social media or spending time with your spouse or kids. And if you choose your family over a long-term project because the project isn't producing happiness... then that might be the right choice for you! :)