For starters, you need to define what you consider success and failure. If it's to make a ton of money, you should probably reconsider your options right there. If it's to spend a bunch of time learning and thinking about a topic that may be something else. If it's just a fun side project (just wrapping up another one of those), that's fine too.
Totally agree. If you focus on the money you'll just be frustrated. I could have made more money spending those hours driving for Lyft instead. I deliberately haven't tracked my hours so I won't be discouraged at my hourly rate. Even spending that time on leetcode could get you a better job and more income.
But, there's nothing quite as satisfying as setting out to do something really difficult and seeing it come together. And unlike most other things in your career where you're part of a team and sharing your success, a book basically rests solely on your shoulders. So it's easy to point to it and truthfully say "I did that".
