User blog comment:Kajune/SPN's redeemed antagonists/@comment-26992577-20160601113705/@comment-1975828-20160605192925

Breaking Sam's faith or hope, I think. Sam, as we all know, wants to keep his brother and is so determined to maintain this that one death will simply spiral him into a hunt for a way to get Dean back. Most people, I believe, would mourn and let go if someone dies, but not Sam.

Sam Winchester will defy the law of nature itself for Dean, something even Death noticed, which is why Death wanted Sam killed first, before he sent Dean away.

Gabriel obviously saw this trait in Sam, and believed, that by "breaking" Sam, it would work. One would call this lesson cruel, and it was, since Gabriel did it with little to no mercy, and in the end, his approach didn't work. Sam didn't break. I'm guessing one hundred deaths wasn't enough.