Raising the price of one good usually causes the price of substitute goods to go up. For example, if the price of wheat goes up because of import duties, the pr

Raising the price of one good usually causes the price of substitute goods to go up. For example, if the price of wheat goes up because of import duties, the price of rice will also go up as people switch from wheat to rice. In the rent control example, many people held on to RC apartments because they were a great deal, even though they weren't where they wanted to live. After RC ended, they moved to apartments they preferred (since there was no longer a big price differential), increasing demand (and thus price) for the originally non-RC apartments.