One of the shortest-lived jobs might be the Pony Express rider, as the service only existed for 19 months. The Pony Express was a means of getting mail from America's heartland to the West Coast during the mid-1800s. Back then, communication between these areas was spotty and took a long time. So three men designed a system of more than 100 stations stretching between Missouri and California.
Some 80 Pony Express riders would race with the mail, changing horses every 10 or so miles (16 kilometers) at a new station. The journey lasted a mere 10 to 13 days in total, with the riders covering about 250 miles (402 kilometers) per 24-hour day. It was certainly hard work; those 80 riders required 400-500 horses [source: Pony Express].
The mail route traveled was difficult and not without many dangers (weather, animals and bandits), so riders earned $50 per month — a princely sum for the time. But the riders deserved the pay; only one delivery failed to reach its destination. Despite its efficiency, the creation of the Pacific Telegraph line, which stretched from Nebraska to California and made the first transcontinental telegraph possible, put an end to the Pony Express. It shuttered in 1861, yet it lives on American legend [sources: HistoryNet, Central Pacific Railroad Photographic History Museum].