I've been using SourceTree for my git interaction recently. I love that it's free, and the fact that I can easily click on hashes to see what happened in a commit is awesome. But recently, I needed to perform a merge. A merge that couldn't be performed automatically.
I scoured the web, trying to understand the right way to merge stuff. Everybody has a different method. I set up opendiff, since I have XCode already installed. I spent about 2 hours trying to get my merge to happen properly.
Finally, I found the result I was looking for. The long and short of this story is that the arrows in the merge point to what you want to keep, not the direction you want to merge.