System Calls Make the World Go Round

I hate to break it to you, but a user application is a helpless brain in a vat

Every interaction with the outside world is mediated by the kernel through system calls. If an app saves a file, writes to the terminal, or opens a TCP connection, the kernel is involved. Apps are regarded as highly suspicious: at best a bug-ridden mess, at worst the malicious brain of an evil genius.

more here..........http://duartes.org/gustavo/blog/post/system-calls/