The great thing about knowledge is that sharing it with others isn't a zero sum game. Unlike sharing a bag of sweets (candy for those of you across the pond) where the more you give away, the less you have yourself. Give away your knowledge and you've still got it yourself
I would actually go further, in sharing your knowledge you gain a deeper understanding, both by explaining it, so having to think more about the subject, and by those you share with asking questions.