As you know, 잘 알고 있듯이, 어린아이들은 치명적이다. means As everyone knows well, children are deadly. There are two usages of 듯이 1. bound noun = as if; like A bound noun used when the following statement is the same or almost the same as the preceding statement. A bound noun used to indicate one's guess or assumption. e.g. 뛸 듯이 기뻐하다. 아는 듯이 말하다. 잡힐 듯이 가깝다. 즐거운 듯이 웃다. 곧 떠날 듯이 보인다. 2. connective ending suffix between two statements = as A connective ending used when the following statement is almost the same to the preceding statement. e.g. 그는 네가 생각하듯이 그렇게 대학자는 아니다 He is not such a great scholar as you think. 음식이 몸을 기르듯이 독서는 정신을 기른다 Reading is to the mind what food is to the body. 네 형이 하듯이 해라 Do as your brother does.