moderators . . . ?

First, please allow me to apologize, as this post may be a deviant from the "sadness and depression" forum, however I find it the most suitable place to pose this question.

Forgive me if I am missing the blatently obvious, but I have been looking at and comparing the differences and likenesses of the locked threads.

Some have been locked for very obvious reasons. However, there are others that I, for the life of me, cannot figure out why they have been locked.

Just out of pure curiousity, I wonder if you could tell me what causes a thread to be locked?

Thank you for your time, and any responses to this post.