Also, elders and peers pass on knowledge to younger people. Children go to school and gain knowledge of science, mathematics, history and many other things. The teachers that teach them also may add in something that they have found out to the children's knowledge, as did the teachers who taught those teachers, and so on until the first teacher, whoever that was. Every new teacher, whether it is a parent, a friend, a stranger, or a professor, passes a little of the knowledge gained from their lives onto others, causing a sort of snowball effect that has gone on since the beginning of time. At times, some person finds something brand new that no one ever supposedly knew, which adds more and more to the snowball of knowledge going down through generations and cultures.
Certain types of knowledge come from the experience of life, not just interactions with others. For instance, a person, who lives in a remote place with no electricity or modern commodities, comes to another country and encounters these modern things, could become quickly confused at his lack of knowledge. Only a minute before entering this place, he considered himself knowledgeable of everything in the world, but found himself lacking. So, to gain more knowledge, he explores and encounters a hot stove. Not knowing that a stove is hot, he touches it, burning his hand. He now has the knowledge that stoves are hot and that he should not touch them. This is gaining knowledge from experience, proving that not all knowledge comes from others.
Knowledge comes in a couple ways. You are born with instincts, which can be considered knowledge. You are taught by interactions with others in you life, and you can gain knowledge from living and experiencing. However, most knowledge does come from interactions with others.