How does trade work?

External question — Personal Finance Stack Exchange Author: user2824371 Original post: https://money.stackexchange.com/questions/128102 License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ Adaptation: HTML converted to plain text; contact email addresses removed. I assume that I trade an asset. I bought it with a price of 650. I sold it with a price of 750. Then, I bought it again with a price of 700. Did I earn because it raised from 650 to 750? Or did I loose because I first bought it with 650 then, I bought the same thing again with higher price (700)? It was already with me. So, why should I buy it with a higher price? I know that I won 50 in the previous example because at the end of the day, I had the asset plus 50. But I need understand when should I buy with a higher price and still win? Does it depend on the peak price where I sell or what? What if I sold it and the prices didn't fell (constantly raising). In this case, I will definitely loose when I buy again, right? So, in this case I should only buy the asset and sell it on emergency only, right?