"The problem with selling high and buying back lower is this: the selling high is pretty easy. The buying back is very hard. Nobody knows how low it will go during the next downslope, so when do you pull the trigger and get back in? After a 5% drop? 10%? 20%? 50%? Given the uncertainty, I find I'm always back in again after only a modest drop, meaning the whole exercise left me richer but not by a meaningful amount."

Yep. I agree.

Plus there is always the scenario where you sell after a runup like this, it goes up another 10% higher after you sell. Then the stock sits in a narrow range for a couple of years while the company performance raises the book value to a point where you buy back in and you would have been better off just holding.

I really do think that there will be opportunities to buy the stock in the future for a better price than it is now, the problem is, I don't know how far into the future that will be and I don't think I would wait until it went too much lower if I had all of that cash sitting around anyway. So by selling now and trying to buy back at lower prices I am trying for small gains while risking missing out on any further upside.

Buffett calls that picking up nickels in from of steamrollers.