Rumination, the tendency to mentally dwell on problems, can lead to depression. Why? “Rumination leads you to think about situations in your life with increasing negativity, interfering with your ability to solve problems. So problems persist or worsen,” explains Susan Nolen-Hoeksema, Ph.D., professor of psychology at Yale University. “This leads to more worry and stress,” she says, “pulling you into a downward spiral that can spur depression.” To sidestep this mood suck, experts suggest distracting yourself with an engrossing activity (like reading an enjoyable book) -- and then later swing into brainstorming mode and come up with a few actionable steps to improve your situation.