The sound of something you didn't know was a key going "click" into its lock is unsettling. It happens to me with research quite a bit. Read and read and read and think and think and think and then get frustrated and start plowing ahead anyway and then.... six, eight, ten months later, or more.... "oh, that's what that handle is for!" And I always feel so thick for not having seen it sooner.

Here's hoping that what is on the other side of the lock is worth the getting to it!