In my opinion domaining is like everything else in life. You get out of it what you put in it.
I got hooked on Godaddy hand reg domains in 2012, and don't even remember what my first domain was.
Spent probably $1,000 in the first year and didn't make a dime. But in 2013 I heard about this thing called Bitcoin so I went and hand registered some GoDaddy domains ,that year invested probably $2,000 and got back about $4000. But through persistence, luck , opportunity and watching trends I seemed to have got better. In 2014 I sold over $70,000. In domains in less than 8 weeks at $1000 to $1500 a pop and my portfolio only had around 500 or 600 hand regs. And this was just using Godaddy as the selling platform. I've never had any huge giant sales but at a 1000 a pop it adds up . And if I can do this with my eighth grade education I'm quite sure you can too . Just read study follow trends what's hot what's not .
You can do it , but the only person that can make it possible is you, no one else. And yes if you quit and leave odds are you'll be back.