I don't know about how many people keep holding, but we just experienced a 30%+ fall in tech stocks (and 25% fall in sp500) last year. I held all my stocks because, well, what else was I going to invest in? And if I don't have a different preferred allocation, then I'm just trying to time the market.

My experience (thankfully not paid for with real money, but fake trading) has shown me I am not good at market timing, particularly knowing when to get back in, so I don't bother trying.

It doesn't really take restraint so much as an acceptance that I will likely not do better than buy & hold. I don't enjoy seeing my balance go down, but I am not close to retirement, so I accept that I need to wait it out to catch market rallies because I am not paying super close attention to markets.