I felt like the movie did not at all capture the essence of the book. Each chapter heading of the book is a statement such as, "If he's not making time for you, he's just not that into you."
It basically spells out the behaviors that we as women try to excuse and says - ABSOLUTELY NOT! If he truly liked you, he would make time for you, he would text you in the morning without you having to ask, he would treat you like a queen, he would remember your birthday, etc. etc.
As a twenty-something when I read it, it took away all the feelings about it being personal. After reading it I was able to just say, "Oh okay, he's not making time for me because he's just not that into me. Maybe I should stop wasting time with someone who isn't that into me."
And in turn, now if I hear a woman saying similar things, I'm like, GIRL he is just not that into you. MOVE ON. Men will string along a woman simply so he can get sex. It's up to us to have enough self esteem to say - if he's not giving me what I need, it's not worth it to keep putting in the effort.