Will theory: They are legislating their own private law.
Economic: We live in a credit economy. Future promises become seen as existing property now. Seen as damaging if they don't go with it. Institutionalized.
Juristic: Feeds from the economic reasoning. How can we justify awarding expectation damages--> what is the underlying justification for this? Reasons for protecting, measuring the damages is both a cure and a prophylaxis.