the propensity to sin

as a kid it always seemed strange that some halachot have to be spelled out. don't kill. don' steal. isn't it obvious? as i have experienced more of life i have realized that there is a reason that these laws are spelled out. one never knows who could end up being a murderer or could steal. or commit adultery.  i haven't done any of these things, but i have met individuals who have. i would never have expected these people to have done these things, but they have. apparently its not as obvious as i once thought. this is why it has to be spelled out and drilled into peoples heads. it is in the hopes that no one will ever engage in such grievous sins.