Here's how it works: At the start of a relationship, a man will get excited and motivated by the challenge of winning a woman's affection. The challenge automatically stimulates the production of testosterone, the "male" hormone that contributes to a man's sense of power and well-being.

As relationship routine sets in, and the challenge in the relationship decreases, however, his testosterone levels naturally decrease. When this happens, the honeymoon is over, and a man starts to look elsewhere to stimulate higher levels of testosterone to make himself feel good.

His workplace will almost always provide new challenges to capture his interest and raise his testosterone levels. Similarly, when a woman gets to know her partner and feels safe with him, there is an increase in the production of oxytocin, known as the "cuddle" hormone. A woman experiences more energy, happiness, flexibility and attraction for her partner when her oxytocin levels rise.

Over time, as reality sets in and her expectations are not always satisfied, she no longer assumes that all her needs will be met. The resulting decrease in hope, trust, and optimism will affect her oxytocin levels.

His detachment and her increased attention to their lack of connection will inevitably build tension in the relationship. If men can learn how to boost their testosterone levels and women their oxytocin through their behaviour, and understand each other's need to do so - their relationship will vastly improve.