Many singles bars have “ladies’ night” where women are offered price discounts. Singles bars do this for women but not for men because (heterosexually-focused) bars are what economists call two-sided markets – platforms that have two distinct user groups and that get more valuable to each group the more the other group joins the platform – and women are apparently harder to attract to singles bars than men.
Businesses that target two-sided markets are extremely hard to build but also extremely hard to compete against once they reach scale. Tech businesses that have created successful two-sided markets include Ebay (sellers and buyers), Google (advertisers and publishers), Paypal (buyers and merchants), and Microsoft (Windows users and developers). In some cases individuals/institutions are consistently on one side (buyers and merchants) while in other cases they fluctuate between sides (Ebay sellers are also often buyers).
In almost every two-sided market, one side is harder to acquire than the other. The most common way to attract the hard side is the ladies’ night strategy: reduce prices for the hard side, even to zero (e.g. Adobe Flash & PDF for end-users), or below zero (e.g. party promotors paying celebrities to attend). Rarer ways to attract the hard side is 1) getting them to invest the platform itself (e.g. Visa & Mastercard), and 2) interoperating with existing hard sides (e.g. Playstation 3 running Playstation 2 games).
If you are starting a company that targets a two-sided market you need to figure out which side is the hard side and then focus your efforts on marketing to that side. Generally, the more asymmetric your market the better, as it allows you to market to each side more in serial than in parallel.