Margin of error

I've learnt a lesson today: Respect the margin of error.

When UPS says they will deliver anytime between 9 am and 12pm, do not, under any circumstances, leave your house till 12.30pm at least.

Margin of error. We're all guilty of it. UPS is no different. They found that 10 minute window in which I wasn't around and turned up. All I have to show for my lack of respect is a slip of paper and a 48 hour wait (tomorrow's a bank holiday).