The difference between the perfume and the furnace

Allah's Messenger (ﷺ) said, "The example of a good companion (who sits with you) in comparison with a bad one, is like that of the musk seller and the blacksmith's bellows (or furnace): from the first you would either buy musk or enjoy its good smell while the bellows would either burn your clothes or your house, or you get a bad nasty smell thereof."