So assuming I am trying to grow the number of stock I have, if I sell at a profit, would the stock have to drop ~20% to ‘buy back in’ ?

Assuming my capital gains tax is 20% for ease of math. If I buy a stock, it goes up, I sell, if I want to buy back in hoping to buy more stock, does it have to drop 20% to actually end up with more? It sure seems that way:

eg:

I buy 10 stocks at 1$. It goes up to 10$, so now 100$. If I sold, id be paying tax on the gains (90) so ~18$. Meaning, I have 82$, the stock would have to fall over 20% so that I could buy back in with more stock. Am I missing something, because this seems pretty insane.