One of my biggest challenges as an entrepreneur is I just can't take the plunge to start a business with no way of making revenue. Even though I can see all around me that that (once again) is how riches are made.
Don't worry, these sorts of companies are just lucky blips. For the most part if you set out to build a new company and you cannot predict where it's revenues will come from the odds are against you.
Keep focused on building a business. It may take longer but you will learn lots more along the way and your chances of success will be greater if you have a revenue model already baked.
There must be something Foursquare are not sharing with us, along with other commenters on this thread I don't know of a single user of their product since 2011.
