That the sexual intercourse of adults appears strange to children who observe it, and arouses fear in them, I dare say is a fact of daily experience. I have explained this fear by the fact that sexual excitement is not mastered by their understanding, and is probably also inacceptable to them because their parents are involved in it. For the same reason this excitement is converted into fear. At a still earlier period of life sexual emotion directed towards the parent of opposite sex does not meet with repression but finds free expression, as we have seen above.
