If you buy a bitcoin in the price of 9000$, yes it may drop, but we have clearly seen that this is what it does. It goes up and down. If you have 1 million dollars and buy 100BTC (900.000$) then the only thing you have to do is wait. Because someday it will pass that number and you will have profit. Am I wrong?
Some people do not have the holding power. If they buy bitcoin with the hope of gaining profit, they want that bitcoin should pump quickly so that they can cash out profits. But if the bitcoin dumps and they do not have the power to hold (due do financial issues), they sell it in loss. That's why it is recommended that we only put small portion of our saving in bitcoins but for long term.