HODL may be dumb, and yes you can cash out and repurchase, but "cashing out and repurchasing" requires timing the market, which generally doesn't work out.

I could've cashed out and repurchased funds in my IRA over the past few months, but that would've required me to be able to predict the future.

> The entire philosophy can be reduced to: if you think it’s going to go up, buy more, otherwise sell.

Isn't this the philosophy behind all investing?