Mark may call his story "good news" (1:1), but Jesus's arrival isn't all it's cracked up to be in the happily-ever-after department. Turns out it will exact extreme suffering and—yes—grief and mourning. This is no story of triumph or health and wealth, but of loss, betrayal, and abandonment, which bring in their wake a sadness that is shared by both characters and ideal readers.
Things get majorly dark at the very end of the story, as the disciples witness their master's arrest and Jesus approaches his painful death. Several allusions to Psalms of lamentation just drive the point home. Break out the tissues.