If someone does not believe in bitcoin, then they might not feel FOMO or even really realize how much they are missing out until several years later, and sometimes it will be necessary to really point out the difference between investing in bitcoin versus other kinds of investments that they could have made before it might start to sink in that bitcoin would have had been a better investment.

Also, sometimes it is not really clear either regarding whether bitcoin is better or not, and several of us who have been into bitcoin longer notice these kinds of longer term trends and even some of us might become a bit wowed by how well a consistent BTC accumulation strategy ended up paying off.. and so it is even more apparent when new ATHs are being made.. but at the same time, if someone is coming in new, it could take them a whole cycle to build up their BTC holdings and even start to really be able to see positive results  (and we know that positive results are not guaranteed, either, so position size has to be accounted for in order to realize that positive results are not guaranteed).