One day a programming novice was writing a general relativity simulation, but his program crashed. He packed his laptop into his backpack, and hiked up the steep woodland path to the mountain abode of Master Foo some 10,000 feet above sea level.
After seeing the crash, Master Foo asked to see the source code. The novice had used the sleep function to synchronize between threads!
The Master motioned to the clock on his mantelpiece. It had already gained five microseconds with respect to the NTP servers at sea level since its synchronization that morning.
"Does your program work near a black hole?" Master Foo asked the novice.
The novice was enlightened. He took his laptop back down to his village and used synchronization primitives 'till the end of his days.