The article explores how different types of companies, like exporters and multinationals, can coexist in a market with varying tariffs. The researchers found that when firms can choose their tariffs, the ones set by countries are usually higher than what would be best for everyone. This leads to less efficient firms being able to survive. Interestingly, having foreign direct investment (FDI) in the market can actually help by reducing the competition between tariffs and improving overall welfare.