when you dont want anymore?
there's always this notion that we're supposed to be "done" one day.
there's a reality to this. if the instrument is purely a tool, and that tool meets the needs of the owner, that's "done." but, a lot of us are closer to collectors than we are working musicians (and lots of us are both.)
I know a few classical players who've had the same bass for 30+ years, its a tool and it does the job and that's it.
I also know of people who collect swiss watches at $10,000 a piece or often a more than triple that, and they have no notion of ever being "done." they enjoy the collecting, buying/selling, trading, having something rare, making a profit selling it three years later, on to something new and unique that their other collector buddies will marvel at, and on it goes.
in comparison to that hobby (or cars, or really anything people collect) what's wrong with bass collecting- especially when some really fine stuff can be had for the $1000 mark, and world class stuff on the used market can be often found at under $2000.
I really like buying and selling basses. I have several that are with me and are very much tools i've used to earn a living. but i always want to check out new stuff, and i don't have any desire to be 'done.' Basses are awesome and the used marked is your friend.