How does the system of checks and balances make it difficult for the congress to pass a law that the president proposes

Congress's power to override the President's veto forms a "balance" between the branches on the lawmaking power ... Congress can override a veto by passing the act by a two-thirds vote in both the House and the Senate. (Usually an act is passed with a simple majority.)

When the president proposes a law it is hard to override that law with a majority vote, being that the president holds a higher office power.