Yep, it is true, never buy a coin just because of the hype. Defi coins are okay, but don't buy them if you don't know the potential in the future. Buying the coins because of the hype, will be too risky for you. The hype will disappear any time, we don't know if the hype may be over tomowrrow. Because of this reason, you only buy if you know well the potentila of the coins.