To the long term, later in life investors… when do you sell?

I began investing about 8 years ago but I was a teenager at the time. I have been lucky enough to have family teach me about money and investing from an early age so I was excited to start.

I did a fair amount of research, and bounced ideas off family and decided to put my little big money into Walmart and Costco.

I still own those stocks today, although trimmed some earnings on Costco because it freaking exploded.
My investing strategy is boring and ofcourse I have expanded my portfolio since then. I plan to hold my stocks for >20 years barring any significant changes to the businesses.

But at what point do you sell? I have other stocks I’ve watched turn from 75% return to now negative in portfolio and I’m happy to slowly add during this bear market.

My question is to the experienced investors – when do you finally sell? It’s in my nature to hold because I believe in the businesses I invest in and don’t want to cough up taxes either.