Even though we are currently in 2013, a very advanced time for humanity, sex is still a taboo subject amongst most people of the world. Although I must say that a lot of women have become confident in this department, and have sort better ways to please their men, some still are shy when it comes to topics related to sex.
To stress the importance of sex in holding a relationship together, I would like to quote Napoleon Hill, from one of the chapters of his bestselling book, Think and Grow Rich-
"If a woman permits her husband to lose interest in her, and become more interested in other women, it is usually because of her ignorance, or indifference toward the subjects of sex, love, and romance...Married people often bicker over a multitude of trivialities. If these are analyzed accurately, the real cause of the trouble will often be found to be indifference, or ignorance on these subjects."
I don't believe that sex is all that matters in a relationship, but it is very important component. People that have overlooked it have found the other things that mattered crumbling, even though they put their best efforts to making things work out.
This is book was written with the main purpose of helping females satisfy their men better, sexually.