What do you suppose he meant by saying "we have probably had too good an opinion of human nature in forming our confederation"?

When George Washington said this in a letter addressed to John Jay on August 15, 1786, he probably meant that when they formed the confederation, they thought of the human nature too upright when in fact not since part of human nature are its negative characteristics such as its being selfish and self-seeking.

By saying "we have probably had too good an opinion of human nature in forming our confederation" he said that, their opinion in examining and classifying the nature of human tendencies is being taken into further knowledge as to forming a certain group attribute that is the confederation.