One of the first thing I remember about my first agent's notes on Deathday was a really great scene at the end between Shane and Ollie where Ollie expresses his love for his best friend. Chris wrote a note telling me that I'd really earned that scene.
That note was something I think about often, especially when I'm trying to hit a really big emotional note. Most recently, I was working on a short story (which, in case you're wondering, is freaking hard!) that has a killer ending. But some of my first readers were concerned that I hadn't earned the ending yet. And I'm pretty sure they were right.
Having a great bit emotional scene doesn't mean anything if the reader isn't right there with you. The scene between Ollie and Shane was earned because I'd spent 80% of the book building their relationship, showing you how close they were. Take, for example, the first scene of Kill Bill Vol. 1. The fight between Kiddo and Vernita is awesome, but the emotions don't mean jack yet because we don't know anything about either character. Tarantino tries to use Vernita's little girl to pull some emotional weight into the scene, but the truth is, he hasn't earned it. We don't care because we haven't been giving a convincing reason to care.
That doesn't mean that the scene is a failure, just that it's a failure as an emotional scene. As a fight scene, it's one of my favorites.
So, as you write your stories (or read them), think about all the things that happened to get you to the big emotional moment in your story. Did your character earn that kiss with blood and sweat and tears? Did she slay the villain because she was in the right place at the right time or because she hacked her way to victory by wading through the blood of 88 Yakuza...and Sophie.
Earn those moments, and your readers will follow you anywhere.