Some ETFs reinvest their gains in the fund so the only way to make money is to sell your holding. What is the right strategy here? when should you sell your ETF holdings? Do you sell them all in once or in steps? Do you buy more of the ETF?
sell them when you need/want the money for something else. same with anything really.
As John said, you don’t sell them unless you need the money. You buy them and hold them long term, adding more money regularly until you retire and need the money.