Why did this plane end up off course

In 1995, the pilots of 727 wound up lost over the Andes mountains in South America. Under pressure to make it to the airport quickly, they began to make mistakes. What started out as a simple lapse in judgement, quickly snowballed into a series of critical errors, each one compounded by the one before it. In a few short minutes, these mistakes would result in the deaths of nearly everyone onboard