This question has caused me so much emotional stress and depression for the past couple years. I've bitched about it thoroughly is some other threads. But, after several near mental breakdowns, I realize that it's just about getting to work and having a solid practice schedule. What else can you do?
I was already a professional EBer before taking up DB, working for a small record label in Nashville as a session player, a ten year regional/national touring career, gigs with some "big-time" country artists, a jazz/funk trio with a small record deal and all that good stuff. I decided though that it was time to pursue my degree at 23 (now 25) as a husband, step-dad and soon-to-be father-father.
Still though, when I picked up the double bass almost three years ago I KNEW that I just wanted to be a section bass player in a couple minor pro orchestras. The first time I really paid attention to an orchestra was seeing a rehearsal of the Nashville symphony playing Bach's toccatta and fugue. I was bloody hooked, bad. But, in this field you are just set up to have that mentality that unless you are starting fresh out of the womb you won't ever have a chance to do anything. Not to mention that a lot of stuff you'll read on the 'net on sites like doublebassblog pretty much tell you that it's not worth the effort and that you'll never 'make it'. My teacher even told me that as a great bassist, I still probably have a better chance of winning the lottery or landing a role in a major hollywood film than getting into a major orchestra. Discouraging, but probably true...
For many people, this could be true, you might be too late...for me it could be true, I don't know yet. I have only taken sevem lessons and have spent the past couple years really working on getting my intonation and basic techniques as solid as possible. My teacher says I'm like swiss cheese; I'm really talented, but I have some holes that need filled in.
So, all this blathering is just to let other people in this situation know that you're not alone. I think it's worth it to try. I know that for me, not trying and not taking the risk would eat at me more than knowing I gave it my all and waiting a few more years to pursue a different career path after my education is complete.
I think that if you're reading this you also have a huge resource that can help you greatly. Reading the DB forums on TB has given me LOADS of info. At any rate, I wish everyone tons of luck--don't forget to enjoy yourself in the first place...even if it's hard to do so with scratchy bow sounds and out of tune notes!