Just because a plan doesn’t go ahead 100% doesn’t mean it failed.
And it doesn’t mean that that planning was a waste of time or that planning is not worth doing ever again (trust me, I’ve heard it all).
In its basic form, planning is about setting an intention. Intentions are aims. And days are always changing, for some people more than others (especially those in highly rich interruption environments). No one can predict what will happen but we can throw an intention loop around some time and aim to get a few things done.
And if something crops up, then plan again, and again. That’s what planning is for. Some people may have to change their approach to planning (ie, how much they aim to get done in an hour or in a day) but that’s okay, that’s learning, that’s growth. That’s facing reality.