Be positive?

Choosing to be positive and having a grateful attitude is going to determine how you're going to live your life.

Yet how does one remain positive when everything is falling apart around you?
I thought about this many times, but i've never gotten an answer.

Choosing to be positive:
I've always told myself to think about things in the most positive way possible.
I thought we could make it, but it didn't happen.
I thought i would be fine, but i have already broken down.