We regret about missing Bitcoin, then about XRP then about Ethereum then Doge then Shiba then Pepe (these are some top of my head and from what I've come across in my crypto term).
Point being there are always new opportunities and dwelling on regrets is futile.
Don't regret. Don't leave a room for shame of yourself. Just remember that there are tons of opportunities in the marketplace and it will never stop. Last year, last month, last week, yesterday was the best day to buy, today is the second best.
Instead, learn from the past opportunities, it is not a mistake that you left out before. It is part of your financial journey. Ask yourself how can you participate if almost the same opportunity present itself. What can you do better?