Alma 42:29

"And now, my son, I desire that ye should let these things trouble you no more, and only let your sins trouble you, with that trouble which shall bring you down unto repentance."

I love this verse.  It simple explains that I should not worry about how others are acting or any other thing that I cannot control.  What I should worry about are my own sins and the need I have to repent and become clean before my Maker.  There's no point worrying about the unknown.  I jest need to exercise faith in those matters and focus on cleansing myself.