I am not a big fan of this whole idea of being a "challenge" with women like some sources of dating advice suggest you should follow. I never advocate waiting for 7 days or longer before you call a woman after you got her number, or making yourself "artificially" and purposely less available than you should be, because I truly believe that one you understand a more fundamental principle of what makes men attractive to women, you won't have to worry about being a challenge. 

And that principles is as follows: a woman developes attraction, romantic and sexual interest and love for a man not so much because of how he treats her but because of who he is. In other words, being sweet, accommodating, kind and generous with a woman is not going to make her more attracted to a guy. On the other hand, when a man demonstrates qualities that make him come across as more masculine - confidence, sense of humor, charisma, physical and mental strength and sexual agression - those qualities will make a woman admire him as an individual more and as a result will make her more attracted to him.  

Moreover, being overly nice, accommodating and kind to a woman will actually lead to the opposite result - it will make a woman less attracted to a guy and even bored with him. I believe that an analogy between sexual encounter and any other interaction between a man and a woman is very helpful to understanding why being too nice with women is a big dating mistake. See, sex, the basic, most fundamental romantic interaction between a man and a woman, is an inherently "dirty" act. It is dirty becuase people and especially women enjoy it most when it's NOT played by the conventional rules. The vast majority of women would much rather being thrown against a walk, put on the kitchen table, have their hair pulled in a public place, being licked from head to tow and being physicially dominated than being handled in a gentle, sweet, overly concerned manner. I strongly believe that the things that a woman wants in her sex life are strongly indicative of what a woman desires to see in her partner - a man who is agressive, decisive, while being an interesting, entertaining and at times unpredictable individual.  

The movie "Flanel Pajamas" is a great example of how a guy who focuses his entire life on a woman's needs and wants without demonstrating and developing his own character will eventually become annoying to his partner, no matter how sweet and humble she might be, and will eventually lose her. I highly recommend that you watch that movie so that you  do not commit the same many mistakes when you meet a great woman who you want to love you and not lose interest in you as your relationship develops and evolves.  

As you watch this movie, notice how the guy says at one point to his wife: "I am sorry, this won't happen again, I promise," and I hope you will be disguisted with hearing that as much as I was. Also, pay special attention how, closer to the end of the movie, he compares himself to his brother and how he correctly points out why his brother is so much more successful at attracting women than he is.