It can go many different ways. You can be 110% invested over years building something (and getting paid for it) for somebody who is ultimately incapable of selling it. It fails, womp womp. You can be 10% invested in a pile of crap (and getting paid for it) for a company that's simply checking the boxes. It fails, womp womp. You can be 90% invested in an ill-conceived idea that actually turns out great (to spec), but ultimately fails, because it wasn't anything anybody EXCEPT the client asked for. Womp womp again! You can even do everything right, do great work for a client, launch it, it performs exactly as was expected, then 3 months later is wiped from the internet because the marketing campaign is over, and a new quarterly budget came in for the client, and then it's on to the next thing.

All of this stuff can be remarkably ephemeral, farts in the wind even, and all you can do is take pride in what you did when you did it, and then take on the next challenge.

Sounds depressing if you frame it up a certain way, but it's actually really freeing to just give in completely to the process and treat it like the weather: you're gonna get everything from sunshine to rain to snow to hurricanes, and none of it is in your control. Just enjoy it while it's good, and ride it out when it's not! There's always something new on the horizon.