One of the reasons why big investors almost never lose their money.
Let's take the case for example, that I have spent 1000 $USDC o USDT on $BNB a 610 USDT each and I have obtained ~1.64 BNB. Then BNB starts to go down to its support point, let's say 560 USDT, that is, -8.93% more or less. So I decide to buy 1000 USDT more and since each BNB is now worth 560 USD I get ~1.78 BNB
Now I have ~3.42 BNB which I have paid 2000 USDT in total. The average purchase price of my BNB now is: 2000 : 3.42 = ~584.80 USDT. It means that to break even, I now need BNB to rise ~4.43% and no longer 8.93%. That is: 584.80 - 560 = 24.80, then (24.80 : 560) x 100 = ~4.43%.
While when the price of BNB rises from 560 to 584.80 USD I will already reach the breakeven point, when the price returns to 610 (the price of the first purchase), I will have a profit of: 3.42 x 610 = 2086.20 - 2000 = 86.20 USD since now I have 3.42 BNB paid 2000 USDT in total. The profit obtained would be ~4.31%, since 2086.20 - 2000 = 86.20 and (86.20 : 2000) x 100 = ~4.31%. Logically you have to subtract commissions and such. What matters is the concept. It is NOT BNB buying advice in particular and at all.