There is an old saying, that sometimes it can be hard to see the forest for the trees. Sometimes you can get so wrapped up discussing a minor point that you can forget why you're discussing it in the first place, or what you plan to do once the difficulty is resolved.

If you think this is happening, sometimes you can help by stepping back and asking how what you're discussing at the moment fits into the larger picture, e.g.,

A: so, we're trying to find out if angles x and y are the same.
A: why do we want to know that again?