I keep thinking why Richard was cross with Locke for choosing the knife as one of his possessions. To choose a knife is all about survival isn't it? A knife can be used to kill for food or to protect yourself from harm so it's a survival weapon.
Strange thing is that when the computer in the Swan station was put out of action, a knife was no use to Locke and they needed Sayid (a techie of sorts) to fix it. Locke was Lost and shouted out: "What am I supposed to do?"
Sayid came to the rescue and Locke was amazed that Sayid didn't ask questions about the broken computer or the countdown.
So you have Jack who hears the explanation of the countdown/computer and dismisses it, Locke totally buys it and with Sayid the why and wherefore wasn't a burning question, he was totally practical and just concentrated on fixing the computer.
There's a message here somewhere!
