Why does paint begin peeling away from a surface in sheets?

Like flaking, peeling results from paint losing its adhesion properties. Often caused by applying thick coatings to poorly prepared surfaces, e.g. unthinned emulsion onto distemper. The cure is to thoroughly scrape back all areas of poorly adhering or defective coatings to a firm edge. Finally, rub down to 'feather' broken edges, dust off and repaint.