The universal principle 'to give to get' has been existing since the birth of the universe. It applies to human's life just as well as to anything. Some may call it 'karma' or give it any other name, but the idea is always the same: you get what you give.
When applying the principle to website optimization, it translates to creating and developing better websites. For existing websites, it means optimizing websites. By allowing your site visitors find what they want easily and quickly and providing pleasant website experience, you 'give'. By having your site visitors buy from you, you 'get'.
Below are some posts that go around the principle of giving to get, when applied to various aspects of website optimization.