Now, this is a hard one. Not a lot of writers can pull this off and be successful at having their audience/readers shed a tear.
But, it's not impossible.
So, in an attempt to help you guys achieve this level of power, I will write a short post about this topic.
To make the audience cry is not about filling your story with sad events. No, that'll just make your audience want to leave the movie theater or your readers put down your book and never open it again (unless, of course, it's meant to be filled with sad events). It's not what happens in the actual sad scene that makes the audience/readers cry, it's the reactions of the characters that are most affected by it.
Take Big Hero 6 as an example. I'm using Big Hero 6 because it's one of the only films that has made me cry real tears. Spoilers up ahead. In one of the scenes leading up to the last, Hiro and Baymax venture into the other dimension to save Abigail. After finding her, during their journey to the exit, Baymax is forced to be left behind as his thrusters were no longer working. That wasn't the part that made me cry. Sure, it made me sad but it wasn't enough to make me cry. What did make me cry was Hiro's broken facial expression as Baymax watched him leave.
However, if the characters in this exact scene were replaced with other characters that I didn't care about, it wouldn't have the same effect. Therefore, you need to make your audience or readers care about your characters before you can make them cry, but I won't go into much detail about that in this post.
So, with all that being said, here's the formula to make the audience cry:
Characters that the audience care about + Sad event + Even sadder character reaction = Audience Tears