There are people who regret for not investing in Bitcoin when it was very affordable and some said they can't afford to miss such opportunity again in their life but yet they are still letting go the opportunity later they will still regret which is a sign of unseriousness and I guess they are still having that same feeling they had some years ago, it's fine to have that feeling but it's not good to go into Bitcoin investment with that feeling because one can easily panic or sell in loss because of the market volatility which is a negative vibe but I understand that everyone must not invest in Bitcoin so anyone who think it's not good for him or her should forget about it and anyone who thinks he or she can do it then its cool.
The reason why they regret is when they see bitcoin market increasing, they just imagine the profit they would have made if they had invested in Bitcoin. This set of people are just interested in the profit but they are not ready to invest maybe because they lack understanding of bitcoin and not discipline enough to start.
To invest bitcoin is more than just interested in making profit, it takes good understanding, discipline patience to invest bitcoin, if you don't have these qualities you will keep regretting always for not investing. Those who are investing in Bitcoin, they are not investing because they have so much money but it is because they have the understanding, discipline and patience and to invest bitcoin with what they can afford by using the DCA method of investing.