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.