  In the first category are the by-product theory proposed by Olson and the possibility that political entrepreneurs, at least partially acting in their own interest, can engineer provisions. In the by-product theory, I might contribute to my group’s effort because the group ties my contribution to provision of some private good that I want, such as participation in the Sierra Club’s outdoor activities or, in the early days of unions, low-cost group-insurance benefits not available in the market. Such private goods can commonly be provided in the market, so that their usefulness may eventually be undercut. Indeed, firms that provide insurance benefits to their employees thereby undercut one of the appeals of union membership. The general decline of American unions in recent decades is partially the result of their success in resolving problems for workers in ways that do not require continuing union effort.