Why regret events that happened in the past if it can't be changed? Regret about the past will only "poison" the present.
You ask this question to understand whether BTC-users have a syndrome of missed opportunity? Because bitcoin in the past and now has a completely different value. If I were in Laszlo's place and bought 2 pizzas for 10,000 BTC (which would make me a millionaire now), I still would not regret it at the moment. Since there is no direct financial damage. At the time of purchasing these pizzas, these 10,000 BTC were worth ridiculous money. And it is not a fact that these 10,000 BTC could be saved to this day.
Lack of financial success is not a loss, and lost profits only mean that you are left with what you have.
I absolutely agree with you. Regretting is pointless. Every action we take in life should allow us to learn something. There is no real loss or failure, there is learning. However, it is true that someone who used BTC to buy anything and everything and who is today in abject poverty could have some regrets.
When I was learning about BTC, I had the equivalent of 2 BTC in shitcoins: none of these coins exist today. It was purely and simply 2 BTC that evaporated.