The term free rider originates from the idea of someone who rides public transportation without paying the fare. The free rider problem is what results when too many people do this: the transit system will go bankrupt. More broadly, the free rider is someone who uses or enjoys the benefits of something without paying, or takes more than his or her share of a public good. Free riders can cause others to curtail their own contributions, not wanting to be taken advantage of. In some cases, the free rider problem is viewed as a necessary cost of government. When citizens pay for national defense or environmental protection, everyone benefits, even those who evade paying taxes.