A hot topic on question-and-answer site Quora recently: Why are so many employees leaving Foursquare, the New York-based check-in startup?

Justin Moore, a former director of engineering at Foursquare who joined Facebook a year ago, offered his own take.

Moore didn’t buy the premise that a lot of people were leaving Foursquare, relatively speaking. He counted 15 out of 150 employees. (The highest-profile departure was cofounder Naveen Selvadurai.)

But his answer shows a key problem for Foursquare, which has many challenges, including drumming up revenues: Where it previously had New York-based engineering talent largely to itself, there are now startups and big companies who are able to compete for the same programmers and offer them similarly challenging work.

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