Consider Fred, who is paid $1 and produces $10 in value. Every employer would love to have Fred come and work for them. In fact, another employer would likely offer Fred $2 to come and generate $10. Fred, not being an idiot, takes the offer.

Another employer offers Fred $3, and so on, until Fred is making ($10 - opportunitycost).

In other words, Fred being way underpaid according to the value he produces is an unstable situation.