1. Rubber Duck Debugging
The first thing I usually do when I hit a wall like this is talk myself through the problem again.
This technique usually works well for me and is equivalent to those times when you ask someone for help but realize the solution while explaining the problem to them.
To save yourself embarrassment (and to let your coworkers keep working uninterrupted), people often substitute an inanimate object, like a rubber duck, instead of a coworker to try and work out the problem on their own.
Alas, in this case explaining the problem to myself didn’t help, so I moved on to the next technique.
This one works more often than you might expect, and is a big part of the value behind pair programming.