Question

Because sometimes we said : " That is true ... why not This is true ? " Or I put the foto on the facebook and I can write what ? .. I love that place or I love this place.

Answer 1

in the sentence when you write 'that is true', you refer BACK.

if you put a photo on facebook, you need to use this because you refer to something that we see, so you need to point to it with 'this'.

Answer 2

It's a question of proximity, whether "in the real world" or emotionally."This" is where the speaker is, and "that" is somewhere away from the speaker.

You ask why you should say "that is true" instead of "this is true" - the answer is you can use both - it depends on how "close" the thing is to you."That is true" sounds more objective, perhaps based on provable facts, whereas "this is true" sounds more subjective - a personal opinion based on your interpretation.

If you're posting a photo on Facebook of a place you have been, again, you can use this or that."That" means you are pointing away from yourself to something that you see as an observer, but "this" suggests that emotionally, for that moment at least, you are there at the place.

One way of comparing them is with "here" and "there". "Which book do you want? THIS one HERE or THAT one THERE?"