I think I'm coming at this from the opposite end to a lot of you older guys (who have done most of the posting here). I started making the effort to be a regular gigging musician about 5 years ago, I got lucky in some respects as I got in with a wedding band that operates like a franchise so has up to 10 bands out on a Saturday night and therefore always needs musicians. This introduced me to a lot of good people and also allowed me to cut my teeth in the wedding/corporate scene. The skills I learnt there have helped me get more of the high paying gigs (allowing more time to practice) and informed a lot of my original music.
I think one of the key differences between those who don't give up and those that do - excluding personal choice and injuries - is that they got in with the better/busier players in town, which leads to better gigs and opportunities, which gives you motivation to do more. I've played with a lot of sub-standard musicians because I wasn't moving in the' good musician' circles at the time. Because I powered through, learned from my mistakes and orchestrated a few situations in my favour, I am now a far more in-demand player. I guess it depends how much bull$#£ you can put up with - hint: it's a lot - and also how self-aware you are. Luck may also play some part in it too...