It's true that there is always a downfall but the problem is when or how long will you wait for it. There is always a sweet spot on every price trend of a certain no matter what the trend is, You can have profit even though you don't wait for the downfall, The only thing you should learn is for how long will this trend will go.
A Pro trader don't buy on the bottom because you can't guarantee if the price is real bottom or not. Traders wait for the confirmation of trend reversal before they enter so meaning they enter during the price recovery and not during the dump period.