When the price of some asset rises way about it's value, we can talk about seeing a bubble in the making. There are many reasons for such bubbles to appear ... it can be a mass hysteria (FOMO), exciting new technology that makes investors act irresponsibly, cheap capital available from central banks, cheap loans ...
We've seen all kind of Bubbles in our history already ... the Tulip bubble that happened in the Netherlands in the 17th century is probably the most often used example, see more details here : https://en.wikipedia.org/wiki/Tulip_mania
We also had several real estate bubbles in several countries, caused by irresponsible banking behavior, there was the DOT COM bubble ... and some people believe Crypto is a bubble too. Time will tell, but we do not share that opinion.