The typical assumptions that are made include the following. They assume a static economy where every economic activity that is reduced causes a permanent economic loss. But in a dynamic economy, especially a growing one, that is not what happens. Expanding economic activities compensate for contracting ones. They assume complete passivity on the part of all economic actors.
Economic actors make no adjustments to minimize the impact of economic changes.
But in a market, entrepreneurial economy, that is not how we respond. Each of acts to protect our interests, and as a result, markets respond to reduce the impact of negative economic changes. They assume that valuable economic resources that become unemployed in one activity become permanently unemployed. But in a market economy that is not what happens. Economic resources, including workers, capital, and land, shift from less profitable activities to more profitable activities.