The reason why is FOMO is bad sometimes because it leads to buy high sell low situation instead of buying low sell high that can lead to excessive loss which happened to me quite a bit during my early crypto days lol.
FOMO can be good (sometimes) but FOMOing on already 200% up projects can be bad IMO.
when you already know that there is a FOMO which has an influence on the price movements of a coin, then my advice is not to enter and participate there because it will make you stuck on that coin and of course some time in the future the price will collapse and become cheap again due to price movements what is generated from FOMO cannot guarantee that it will keep going up.