Possible daily returns can be expressed as a percentage. The average of these outcomes is higher than 0%, meaning every day that you are long, on average, your will have more than 0% daily return.
Selling with the intention of buying back is the same as naked short selling with no intention of being long. For a short seller, the average daily return is the exact opposite which is less than 0% daily return. This means that if you sell and hope to buy back lower, you might end up in a situation where the daily returns have a string a positive gains, making it that much harder for the price to come back to a profitable level. For example, selling at 2.5K last year and seeing price go all the way to 20K.
Selling without the intention of buying back is a different position since you will take the money and never put it back in the instrument. In this case, future daily returns are meaningless. However, that's rarely in play except when you retire and decide to be out of the market entirely or you die.