Berkshire files form 13F with the SEC that anyone can read.

He sells.

Serious question, when you're accumulating more assets and haven't retired yet, why is it a problem to never sell?

My expectation of a typical HN reader is that they are saving for more things/experiences/goals, not just retirement.

I'm curious why you would have that impression and why you think investing is the way to achieve those things.

Nothing saved for the short term should be in stocks. That would be an easy way to lose 30% of your vacation fund I'd you needed to sell on a dip.

Probably true, but I would also assume most readers are not putting all of their investments into one single fund for retirement.