This and That

I have been wondering this question my entire life, and I want it to be answered: At what point does this become that?

Is something "this" as long as it is within arm's reach?

Is something "that" as long as it's just out of reach?

Say a person is standing next to a tree. Is it more appropriate to associate the description of "this" or "that" with it? This tree. That tree.

These are the things that frustrate me on a daily basis.