Can someone explain positional value?

[Time's Yours]

Obviously, I get the basic concept. Quarterback is the most important position, fullback is the least. But what about everything in between? Why is a left tackle more important than a left guard or right tackle? Why not take an LB with a top-5 pick? What is the general heirarchy of positions?

1. QB
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DE/DT/LT/HB?
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22. Fullback
23. Kicker
24. Punter


Edit: I forgot my post requirements. Your and idiot, and Fire Herm!!!