Good question, as much about life as it is about pool. An old saying is that you should always plan for the inevitable. In pool, the inevitable includes long trips to the chair. Embrace that it's part of the game and keep your focus so that you're ready when your turn comes. After all, even though your next turn may be ten minutes away, it also may come thirty seconds from now. Best to assume that your opponent will have stretches of brilliance so that when it happens you're not bothered much by it.
The ability to stay in the moment even while opponent has you stuck in the chair is part of pool's mental game.
I agree it’s important to pay attention to what’s going on. If your opponent is a good player, you can always learn something new by watching. The only time I find it hard is if I’m playing an agonizingly slow player, then it’s very hard to watch their entire pre-shot routine.
Of course anytime I’m not playing well and frustrated with my own game, that always makes it harder waiting and hoping for your next chance at the table, to try to turn things around. Sometimes you get that chance and sometimes you don’t.
The other thing that is tough while in your chair, is seeing your opponent get lucky on a key shot with either slopping in a ball or getting a perfect snooker leave when that was the last thing on their mind. You have to try to not show any outward frustration when that happens, and sometimes that’s hard to do when it happens numerous times in the same match.