I have no problem selling guns that I am done with, even if I "lose money" on the transaction. (I say it that way because the money is already gone whether you keep the gun or sell it, so you don't lose any money when selling.)
A few years ago I picked up a Walther PPS M2 that I planned to make my primary carry piece. I bought a few different holsters, more magazines, a mag carrier, etc. Then when I started practicing with it, it turned out that I didn't shoot it very well. After 600 rounds, I was still shooting better with a little Keltec .380.
The PPS never did make it into regular carry for me, and so I put it up in the classifieds, and and it sold the same day. I put that money into magazines, holsters, and a mag carrier for something I can shoot.
You all can keep guns that you have no use for, I guess, but I try not to do that with anything (vehicles, clothing, camping gear, etc.), so I don't do it with guns either.
Your conflating financial value and use. If you have a use for something, then you're going to use your money back out of it. If you have no use for something, then you wasted your money when you bought it.
This is basically how I explain putting money into valueless cars to people. I will get my money back through use.
Really... I'm starting to think the take away here is to practice with any suspected new carry gun for quite awhile before you end up upside down on accessories like holsters and mags. Dump a few hundred rounds through it and if it's not for you, by all means, dump it.
Right now I have 3 carry guns in the rotation. Glock 21, Ruger P90, Ruger LC9. They all fit unique roles so I keep them around and in that rotation for a reason. I bought them all knowing what the task was in the beginning and if they didn't suit the task, I would have kept shopping or sold them almost immediately. Fortunately I was able to try before I buy with all of those, so, it worked out. I just can't imagine carrying a gun for a year or two and then being like "well... this was dumb". Just not my thought process, personally.