Buffy’s decision to remove Spike’s chip
When Buffy chooses to remove Spike’s chip in S7E14, giving him a second chance at being good (despite Giles protests and concerns), Buffy justifies her decision by telling Giles to trust her.
In S7E17 (Lies My Parents Told Me), Giles and Principal Wood try to kill Spike. If the chip was repaired instead of removed, Spike would have been killed by Wood and thus not have been there to make his sacrifice in the final episode. He wouldn’t have been there to encourage Buffy when they gave up on her. Buffy’s decision was not only important for Spike, it was important for the entire mission.
This just fuels my love and awe of Buffy. There was no way she could have known that Spike would play such a big role both in the end and with Buffy herself, other than having so much trust in her intuition and in Spike. She was the only one that knew that he’d use his power for good before it even happened. She thought of him as a warrior and champion despite everything.