Despite being at my laptop for more than three hours last night, I only ended up writing one scene. I wrote a few paragraphs, then realized that wasn't what I was trying to convey, then wrote a few more. Those inevitably were devoured by the delete button, and on and on the process went.
This was a pivotal scene. All the elements needed to be exactly right. And the only way I was going to get it right was to write it over and over again. So I did.
When I finally shut off the laptop last night - somewhere after 11 p.m. - I was quite satisfied with my work. Sure, it took me awhile. But such important scenes deserve more of our attention. If we don't get it right, then the rest of the story will collapse around it. Think of pivotal scenes - the black moment or a character revelation or a revealing plot point - as the steel beams in your novel. If they're not strong, the rest of the story will be rather flimsy.
When was the last time you tackled a particularly tough scene? How did you get through it?