"Our whole culture is based on the appetite for buying, on the idea of a mutually favorable exchange. .... For the man an attractive girl - and for the woman an attractive man - are the prizes they are after. 'attractive' usually means a nice package of qualities which are popular and sought after on the personality market. What specifically makes a person attractive depends on the fashion of the time, physically as well as mentally. ... Two persons thus fall in love when they feel they have found the best object available on the market, considering the limitations of their own exchange values."