Selling and rebuying lower is a very risky move, you don't know when it will go up and you don't know when it will go down so its as risky as holding as well.
Maybe you sold at 12 to buy again at 10 but maybe you sold at 10 and it goes to 12, you never know which one we are in right now until we actually see it happening. That is why people keep saying hold your currency unless you really need to cash out, if there is something like medical or something bill then yeah sure but if that doesn't happen then you really need to hold it because long term holding is the only guaranteed method of making money.
Bitcoin is pegged at dollar right now mostly and we calculate the price on dollars all around the world but dollar loses its value every year, 100 dollars is never 100 dollars, what you can buy with it changes every single year and difference is bigger if you look at decades, so bitcoin holding for long term will eventually profit you in the end.
true but things are never that easy.
there are times in the market, when the trend is more predictable than other times. for example right now it is not so much predictable. all we know is that price is going sideways between $9500 and $11000 and unless it starts going above $12k we can't do any trades for sure.
but for instance when price first hit $12k+ if you sold there (as a short term trader not an investor) then it was a good choice then you could enter your accumulation phase where you bought incrementally between $9.5k and $10.5k and wait for the sideways to end.