How can something so simple, a rubberband, be so effective?

Since I retired from my police department, I have had a problem with anger management with myself. My wife suggested I see a therapist. I did. My therapist tells me that while being an active police officer, that I had suppressed many different feelings, concerning the people I had to arrest and some of the terrible deaths i had witnessed in 44 years. That these feelings are just now surfacing, since I retired. My therapist has been a great help for me to understand why I do and say things, in an angry tone. At first, she suggested medication for me. Not being a pill-taker, I asked if there was another choice. She said, “yes’. She gave me a rubber band. “What do i do with this?”, I asked. She told me to place the rubber band on my wrist. The next time I felt anger approaching me, to reach for the rubber band and pull hard to let it sting my wrist. The object is to refocus my anger and channel it to somewhere else. I really had my doubts. For two weeks I have flipped this rubber band so many times, that I now need a replacement. Guess what? It works! Question: How can something, so simple as a rubber band, redirect a persons thinking and control their anger?