A get-rich-quick scheme is a plan to obtain high rates of return for a small investment. The term "get rich quick" has been used to describe shady investments since at least the early 20th century.Most schemes create an impression that participants can obtain this high rate of return with little risk, and with little skill, effort, or time. Get-rich-quick schemes often assert that wealth can be obtained by working at home. Legal and quasi-legal get-rich-quick schemes are frequently advertised on infomercials and in magazines and newspapers. Illegal schemes or scams are often advertised through spam or cold calling. Some forms of advertising for these schemes market books or compact discs about getting rich quick rather than asking participants to invest directly in a concrete scheme. Obviously, it is theoretically possible to get rich both quickly and legally if one is prepared to accept very high levels of risk – this is the premise of the gambling industry. However, a key difference between legal, regulated gambling and get-rich quick schemes is that the near-certainty of a gambler completely losing the original stake over the long term (even if it offers regular wins along the way) is known (and expected to be accepted) to the players, furthermore nearly all jurisdictions which allow legalized gambling in any form require casinos and other licensed gaming promoters to disclose these risks as part of their responsible gambling initiatives. Economic theory states that all opportunities for profit which are truly risk-free are unstable because they will quickly be exploited by arbitrageurs.