"Perspective" literally means the artist's technique of drawing distant objects smaller than closer objects, the same way they appear to the eye or to a camera. So, to an artist, it means to draw things the appropriate size. Figuratively, it means to consider how important or how unimportant things really are, objectively. For example, suppose you are waiting in line at a movie theatre and somebody cuts in ahead of you. Ten minutes later, you are in the theatre and seated in good seats. But you are still talking, complaining, fussing, about it. Your companion says to you, "Calm down! You're blowing this all out of proportion! Yes, that person is a jerk, but we're here, we have good seats. Don't let it stop you from enjoying the movie. It's a small thing! Enjoying the movie is the big thing. Keep your sense of perspective!"

"Sense of perspective" means to be objective in your evaluation of something. In the examples above, to be objective in our evaluations of what a person has done, like considering the pluses and minuses.

Clouded judgement from not seeing a situation for what it truly is. Stepping back (figuratively) and evaluating a situation.