Madison had a pessimistic view on human nature. He believed that people are inherently driven by self-interest. In his view, if humans were good, then government would not even be necessary. Given that people were naturally self-interested, Madison considered it necessary to reflect this in government.
His view impacted the drafting of the Constitution given that it included principles that were aimed at mitigating against the self-interested nature of humans. This include the principles of Separation of powers, checks and balances, federalism aimed at ensuring that there was no single center of power.