Theory is wonderful.
Nearly everyone is able to accept an idea, concept, situation or construct in theoretical terms. Pontification is easy when speaking of something in the abstract. We may tell ourselves we've accepted something and then: Surprise! Life gets the last laugh on us and throws us a real situation, something our egos have told us we are "ok" with -- and suddenly we're not as ok with it. In fact, we can be downright thrown for a loop by it.
When it's summer and perennial flowers are everywhere, of course it's easy to say "oh yes, I understand they'll only be here for a short time. I'm ok with that and look forward to seeing them next year". What if they never, ever came back? Hm.. that's a completely different story.
I think it's a part of human nature to be resistant to change, particularly if it's not something we've initiated ourselves, or can't control.
Maybe the lesson here is not so much to attempt to master any of the tough theoretical concepts but to realize that we shouldn't be lulled into a false sense of thinking that we have. There are always issues that are going to cause us discomfort; the best we can do is to sit with them and the sensation of discomfort each time they come up and be grateful for the humbling reminder that we are only human.