Remember the computer programmer in Jurassic Park? He was a rotund loner whose workstation was littered with soda cans and empty potato chip bags. The Hollywood stereotype of software engineers is The Lone Coder, a social misfit who shuns human interaction. He can make magic happen with a few clicks of his mouse, but he probably does it from the solitude of his parents' basement.
In real life, The Lone Coder makes mistakes -- lots of mistakes. Answerable to no one, The Lone Coder designs a system only he can understand, and no one else has a prayer of maintaining or modifying. The Lone Coder is a threat to the growth, security, and stability of a computer system. Scariest of all, entire software "teams" can be full of Lone Coders, each one marching to his own beat, following her own whims, leaving a cloud of chaos behind in their wake. Their product might work, but it is a house of cards.