From his post here:

Most of the political economy and development literature seems to focus on national formal institutions, like courts and constitutions and executive constraints. Obviously important stuff. But less talked about are informal institutions like norms of acceptable behavior, how those come about and get enforced, and how (perhaps more importantly) they get internalized–meaning we punish ourselves if we violate them, rather than fearing what others will do. Internalization is handy because it means society doesn’t have sanction people in costly ways.

My posts on the subject (an ongoing series, mostly mini-case studies) can be found starting here.