Tariff
A tariff is called an optimal tariff if it's set to maximize the welfare of the country imposing the tariff. It is a tariff derived by the intersection between the "trade indifference curve" of that country and the offer curve of another country. In this case, the welfare of the other country grows worse simultaneously, thus the policy is a kind of "beggar thy neighbor policy". If the offer curve of the other country is a line through the origin point, the original country is in the "condition of a small country", so any tariff worsens the welfare of the original country.
Tariff
Thus, theory can very easily recommend a trade policy that gives us the highest possible standard of living in the short term but none in the long term. This is what happens when a nation runs a trade deficit, which necessarily means that it goes into debt with foreigners or sells its existing assets to them. Thus, the nation applies a frenzy of consumption in the short term followed by a long-term decline.