a very classic words, buy cheap and sell high, I think it can not be identified with bitcoin alone, a natural thing in life. almost in every business we have, we always imagine a higher return from the capital we have. however, it is not easy. not everything we imagine come true, all through a long process.
Isn't that the main concept in trading. And indeed this concept is the most effective among other concepts. although the pattern is normal, I think here we all apply it. so there is no classic word, because it is impossible to buy at a high price and sell at a low price. lol
All activities are transactions, the basic concept of trading will remain the same "buy low, sell high" if you use the opposite concept, you are not a trader.
There will be still some people who will buy even a certain coin is having a HIGH PRICE in the market, that is because of FOMO or fear of missing out, sometimes even the coin price is high it is good to buy it, but be sure that it will not goes down so instantly, so you should learn how to monitor it and read charts so that you don't have any regrets in the future.