What bad decision does Antonio make regarding borrowing money in Merchant of Venice?

Antonio doesn't have the money to lend his friend Bassiano, and decides to borrow it from Shylock at interest, using ships he expects to return soon as credit. Shylock, feigning friendship, agrees to lend him the money interest-free. He only has to sign a paper before a lawyer that Shylock may cut a pound of flesh from Antonio's body should he not pay the debt on time. Antonio agrees.