I often use this metaphor with clients to convey the counterproductivity of cognitive and emotional avoidance. It is similar to the Pink Elephants metaphor but also suggests the alternatives of acceptance and willingness.
Imagine what you're doing with these (thoughts/distressing memories/feelings) is like fighting with a ball in a pool. You don't like them, you don't want them and you want them out of your life. So you try and push this ball under water and out of your consciousness. However, the ball keeps floating back to the surface, so you have to keep pushing it down or holding it under the water. This struggling with the ball keeps it close to you and is tiring and futile. If you were to let go the ball, it would pop up, float on the surface near you and you probably wouldn't like it. But if you let it float there for a while, with your hands off, it would enventually drift away and out of your life. And even if it didn't, at least you'd be better able to enjoy your swim rather than spending your time fighting!
I hope you find this is helpful.