Market crash always has a lesson to teach us, especially for the greedy people who were in huge profit but were still holding hoping so they can make more profits, one of the major lesson or fact we need to understand is that the market doesn't always go up forever, at one oint a reversal is likely to happen and sometimes and it can be really bad like in 2017, acknowledging that fact should help us know that when the market has pumped way too much then its time to take profits and wait to see the next movement rather than continue holding till the market crash.