From a constructivist point of view, people actively construct new knowledge as they interact with their environments.
Everything you read, see, hear, feel, and touch is tested against your prior knowledge and if it is viable within your mental world, may form new knowledge you carry with you. Knowledge is strengthened if you can use it successfully in your wider environment. You are not just a memory bank passively absorbing information, nor can knowledge be "transmitted" to you just by reading something or listening to someone.
This is not to say you can't learn anything from reading a web page or watching a lecture, obviously you can, it's just pointing out that there is more interpretation going on than a transfer of information from one brain to another.
