According to this book, there are five different ways that people choose to express their affection towards each other (Physical Touch, Quality Time, Words of Affirmation, Acts of Service, Gift Receiving). You might not feel loved or cared for in a relationship if you and your partner have different languages of affection. This is equivalent to people speaking of the same things but not understanding each other due to a language barrier. Being aware of these differences can help you learn the love language of your partner. This book provides a useful tactical model for thinking about relationships, but I wouldn't call it an essential read.
Our most basic emotional need is not to fall in love but to be genuinely loved by another, to know a love that grows out of reason and choice, not instinct. I need to be loved by someone who chooses to love me, who sees in me something worth loving. That kind of love requires effort and discipline. It is the choice to expend energy in an effort to benefit the other person, knowing that if his or her life is enriched by your effort, you too will find a sense of satisfaction—the satisfaction of having genuinely.