It's every child's most common question... and most important. Answers to "why?" reinforce learning. They provide logic, understanding, rationale, and comprehension. Merely knowing what to do and how to do it isn't enough. Why makes the how and the what make sense.
Answers to why? aren't just for kids learning about hot stoves, electrical outlets and running with sticks. Learning at any age doesn't work well without knowing why. Try telling your blood collection staff what the order of draw is and how to follow it without explaining why it's necessary. Those who don't know additives carry over and contaminate the next tube aren't likely to think the order in which tubes are filled really matters. Directives without reasons don't stick as well as those that do.
The same goes for explaining why they shouldn't leave the tourniquet on longer than one minute (causes hemoconcentration), tell patients to pump their fist (falsely elevates potassium results), or chill blue tops after filling (cold changes the test result and leads physicians to reduce blood thinner dosage with disastrous consequences).
Even when we know the why, it doesn't always modify behavior. Children will still touch the burner to see if it's really hot. (It looks the same as it does when it's cold.) Those who draw blood will still have patients pump their fist. (They've always done it that way and nobody's ever suffered from the consequences before... that they know of.)
Whenever instruction includes the what, how and why and still doesn't change one's behavior, there's only one response left for those in positions of authority. It's the same response our parents used when their answers weren't good enough.
"Because I said so."