Did it ever occur to a vanilla partner that pain and suffering is a gift? Well, bit of a leap there. The link is endorphins. They are drugs. And they make you feel great. The best bit is that you can't get arrested for possession. These little chemicals are perfectly legal. You see, they are manufactured by the body. Oh yeah!
Don't get me wrong. I've never taken anything that wasn't perscribed by a Doctor. I can't see why anyone would want to risk 'highs', if they didn't personnally know the chemist was compitent. Not to mention the resulting conversations with the constablary.
Meanwhile, back at the endorphin rush. The body produces these little darlings when you have an orgasm, when you get injured, or are in pain. They are even produced when you do sports, or have a tough session at the gym. They are natures little pain killers. So, first the pain, then the bliss; got it? Now you know why all those guys pump iron, or go long-distant running. For those reading this, it's probaly a large part of why you enjoy a good spanking. (Ah, hot crossed buns!)
Word of warning: Too much good is bad. Like any drug, the resulting highs can be addictive. (Obsessive Compulsive here!) It is why people like David Duchovny ended up in Sex Addiction rehab. As long as you can recognise the down, when your partner is away, for example, you should be okay. It is more upsetting to go through this when you have no idea what it is.
Anyway... Sod the roses, just give me the thorns!