When I think about a new technology, I like to come up with a "proof" that something is or is not substantial. Something like "Email transfers a message just as well as a letter, but is orders of magnitude faster. Therefore, email has substantial value".
For Bitcoin (and other crypto), I came up with this "proof" that it is not a fad:
You can freely buy all kinds of stuff everywhere. A company can sell you a bag of stones. A hammer. A knife. A pencil. A lamp. But you cannot buy Bitcoin freely anywhere. If you want to buy Bitcoin, the government jumps in and says "Oh no! This is extremely dangerous! Write down the identity of this person. We need to monitor them!".
If Bitcoin is so dangerous to governments, it cannot be just a fad.