Impermanence: How do we know when a thing ends or if it's just changing? It seems to be a big deal that we see things as they are. If we are merely assuming when things begin and end or change then how do we ever really see things as they are?
Great question.

From Mahayana perspective "things" do not "end", nor do they "change" - because separate self-identical things are imputations of the mind. In reality things do not have firm spatial and temporal boundaries. Things do not by themselves have identities that stay unchanged throughout their lifecycle, allowing us to designate it as "still the same thing, just changed a little". These identities are chosen by us. So to speak of any "thing", "ending", "changing but still staying itself" - is a simplification. Ontological reality has nothing like that, it is totally up to observers to define "things" in space and time.

How do we "see things as they are" then? We see them with our "wisdom eye" (wink wink).

We remind to ourselves that what we see is not all there's to it, until we are used to seeing it all. For a trivial example, when someone dies, we say: it only looks like this person ended, but that is not true - there are children, books, students, flowers, social influence - whatever imprints they left on the world - it lives on.

When we practice this enough we get in the habit of seeing "energies", "influences", "connections", "processes" behind things. We no longer see separate things, we see the matrix - and that's called "seeing things as they are".

From Mahayana perspective, this is the real nature of Impermanence: everything is continuously in flux, but the mind grasps after "entities" that it itself designates, and then gets upset when these imputed entities morph beyond recognition, like the cloud figures.