Maybe the decreasing price after buying would not be that matter (until you don't buy, as hypothetical example, a bitcoin costing 100 thousand dollars in a specific moment and suddelnly the price goes to 1000), but the way we store cryptocurrencies:
1) in a not so realible wallet/exchange that scams, taking away our cryptocurrencies or
2) we didn't pay attention to the seed when we choose an app wallet we own the keys, our device break up and we can't recover the wallet in our new device because we lost the seed, don't remember it, etc.