Cold showers have been mentioned by many successful rebooters because they work. Whether you are rebooting or not, it can be a highly effective routine for having a more relaxed and badass outlook on life, like meditating. If you go to yourbrainonporn.com, you can find an interview that Gary did with a chemical engineer, who talks about the physiological and psychological benefits of cold showers. One of these benefits is dopamine receptor up-regulation. It doesn't necessarily cause a blast in dopamine, it just produces more receptors for your neurons to transmit the signal of dopamine faster. It can also make you more resilient to stress. Believe it or not, our body's have natural physiological processes that have evolved over millions of years to counteract cold water. This is because our ancestors bathed and swam in it (we haven't had central heating until about the last century and a half.) The idea is that you introduce stress into your life for ~5 minutes each morning and, overtime, your body and mind learn how to process it for long-term benefits. It's the opposite of addiction. With porn, you feel pleasure followed by pain. With cold showers, you feel pain followed by pleasure. There's plenty of other benefits like depression relief, weight loss, and increased energy.