I am the ideal picture of buy and hold. What pisses me off is when I'm forced to sell into cash and then buy in later.
For example, rolling 401k from an old employer to new one - must liquidate to cash, get a check, and the deposit to new provider. That can take a few weeks to do. In between that time, the markets could have changed a lot, depending on the news.
Also, moving money from an old HSA investment account to a new one, same thing, must sell and then buy in later. Weeks long process.
Not to mention all the potential expense of liquidating and buying into new funds, etc., on top of the market swings. I wish there were more direct investment to investment rollovers, or at least more instantaneous electronic transfers that minimize the risk of taking a large amount into cash for a period of time.