economics terminology

Sunk costs
When what is done cannot be undone. Sunk costs are costs that have been incurred and cannot be reversed, for example, spending on ADVERTISING or researching a product idea. They can be a barrier to entry. If potential entrants would have to incur similar costs, which would not be recoverable if the entry failed, they may be scared off.

Barriers to entry (or exit)
How firms keep out competition--an important source of incumbent advantage. There are four main sorts of barriers.
*A firm may own a crucial resource, such as an oil well, or it may have an exclusive operating licence, for instance, to broadcast on a particular radio wavelength.
*A big firm with economies of scale may have a significant competitive advantage because it can produce a large output at lower costs than can a smaller potential rival.
*An incumbent firm may make it hard for a would-be entrant by incurring huge sunk costs, spending lots of money on things such as advertising, which any rival must match to compete effectively but which have no value if the attempt to compete should fail.
*Powerful firms can discourage entry by raising exit costs, for example, by making it an industry norm to hire workers on long-term contracts, which make firing an expensive process.

... Is there a theory to account for when one should cut one´s losses?