The much better approach to the idea of “stop when you’ve won” is called Value Averaging.
The idea there is you have your target and you have your return estimate that you need to get there. In a boom, you sell stocks to keep the portfolio on track, then when it busts, you reinvest those profits to get it back on track. That way you’re selling high(er than you need) and buying low(er than you need).
That way you also don’t need to guess whether a year has been “absolutely spectacular” or not, it’s all defined by your spreadsheet.
