Why Was The Boeing 737-900 A Failure?

The Boeing 737 was, until recently, the most delivered jet-powered airliner of all time. It was developed into four distinct generations, and the third-generation 737NG is the most common of the four, with deliveries of the even more popular 737 MAX still ongoing. The 737NG was designed to go head-to-head against the Airbus A320 family, and for the most part, it succeeded, as, year over year, 737NG sales routinely matched those of the A320.