My biggest regret is when I got introduced to this back in 2012, I tried to buy £200 worth, the platform was down and I never bothered, just recently woke up to it again at over £4k per coin, it is a physiological thing where I don't want to buy at that price.
My most regrettable thing about Bitcoin is probably that I did not know Bitcoin any sooner and invested more in it. Besides, I regret that I sold a lot of BTC at a very cheap price, only one-twenty of the current price. So, now, I do not even have a BTC anymore, that really makes me regret