This depends on the instrument and your location. If you play a popular instrument (say the violin) in a metro area with just one orchestra (some have zero!) then you ain't getting on that orchestra any way short of nepotism. If you live within commuting distance of multiple orchestras, there are more spots, but you still aren't going to be playing violin in the orchestra, and it's even possible that nepotism won't help you.
Also (though perhaps closer to a privilege issue than a nepotism issue):
How did you find the teacher who helped you get ready for the audition?
How did you "pay" for the practice time to prepare for the audition?
Also networking, if you do gigs in the same region the orchestra is located you're bound to bump into a few of the members.
You can also just email the orchestra and ask when they hold auditions.
Some very lucky others that do well are from multiple generations of musicians that were essentially born, bred, and raised to be among the world's best and live and breathe music. There was no way I could ever compete with these kinds of folks and the hard life I saw so many talented people including professors that _are_ established after decades to live a very modest life made it clear to me that it wasn't something I should do for a living despite how much I love and respect it all. My role I feel is to support these folks now, so I go to shows, buy merch at the show, etc. and try not to take up space or attention too much and let people do what they do while trying to show appreciation for the work I was too chickenshit to ever do.
The arts and now entertainment fields are very much "tournament" style careers where given very limited public attention the winners take basically all and the remainder struggle quite a lot. It's nothing like professional fields like tech, accounting, medicine, law, or trades like construction, hospitality. In fact, any field that becomes more mass market-driven seems to become substantially more "tournament" style which has greatly impacted sex work - a top n% take an increasingly higher percentage away from an elastic but fundamentally highly dynamic demand.
The misattributed quote "find what you love and let it kill you" is the typical path of the career musician like most arts. I prefer to at least have some money to have more options to make it more fun on the way without resorting to the trap that is recreational substances.
From the outside it feels somewhat more doable to be a pro , then a band or solo-artist, since there are quite a few orchestra's around that hire people on a stable basis. Spots are limited, but it's not super hard.