Body building techniques isn't all about physical fitness there's a mental side as well. When things are going bad for us we may not keep our commitment to get to gym and even if we do our workout would likely lack the normal intensity. Stress and depression also lead to low testosterone levels which is definitely not desirable for people trying to build muscle.

Try to compartmentalize your feelings. Imagine putting your stress into a box, closing it up and placing it on a shelf to deal with later. I thought this sounded kinda lame when I first heard it but after trying it I found it effective much of the time.

Also, keep things in perspective, most of us have it pretty good, really, and if you think you don't watch this video.