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).
Well, those who have belief issues with Bitcoin are doing harm to themselves. With so much data available about bitcoin that clearly tells how Bitcoin price has gone up from zero dollars to 70k in 13 years. There are online calculators available that tells you what benefit in past DCA and Lump Sum has given to investors. After going through all that data if somebody still has belief or trust issues with Bitcoin then we must not waste time in convincing that guy about Bitcoin.
But I tell you one thing that more you go into Bitcoin more is your belief. As you go on investing in Bitcoin and try new techniques then your belief got more strengthen about Bitcoin.
Most people are just being mislead, like my self back then didn't have any believe in bitcoin I was only engaging with some shitcoins (wasting my time and funds) , having the mindset that I could become rich overnight when engaging with different shit coins but I at the end I got myself rekt. So ever since then have learned my lesson, I decided to know more about bitcoin, and as I continue I became more passionate about it (bitcoin) , so most time I normally have this thought that , had I known I wouldn't have waste my funds in some shitcoins back then I would have invested it in bitcoin and would be in far more better profit that I am in now , but well I know if I continue my DCA strategies and other related strategies in accumulating bitcoin, I would definitely build a good and portfolio for myself even though it may take a whole cycle. So those that haven't started yet (no coiners) is still early for you to embark in this journey of accumulating bitcoin.