There is a scene in Interstellar where Cooper returns to the ship after spending a few hours on a planet in a high gravitational field. Because of gravitational time dilation, the few hours he spent on the planet corresponded to twenty-three years of Earth time. He returns to the ship to to find twenty-three years of video messages waiting for him from his children, who he is longing to get back to. Twenty-three years of life, gone in an instant, watching the people he loved grow and change and live.
I cried at that scene. I rarely cry in movies but I cried at that scene. Not because of the love he had for his children; not because he knew that he had missed all the important things in their lives. But because he had to watch from outside, and know that he could never be a part of it.