Selling is far and away the hardest aspect of investing. I will be loathe to sell businesses that consistently exceed expectations, partly because they are likely to continue to perform but mostly because I am simply not skilled enough to be as active as you implied.
As an example, I have resisted calls for selling my top performer, ALU, for quite a while now. It looks very expensive on a number of measures as things stand. On the flip side, I have a few underperformers that have eroded shareholder value (ISD is one you will be familiar with) simply because I have been too stubborn to sell them.
If you, after 20 years of doing this (and doing it so well with all the evidence I have) have not puzzled this issue out, I (with less than 3 years under my belt) have next to no chance!
In any case, I continue to follow your posts with great interest. Please keep them coming!