Although fiction may take this a little far, it is realistic: Real Life tanks and other armored vehicles are weak on the top, bottom, and rear, but stronger on the front and sides. Hence, in World War 2, special vehicles called "tank destroyers" were tasked with the job of outflanking enemy tanks and destroying from behind. Nowadays, helicopter gunships or infantry with anti-tank rocket launchers do this job. Anti-tank missiles often fly above the tank and come down at it, instead of going straight at it. And if you go back further, by the 1400's, European armour had developed to the point where the entire body could be covered in metal plating, making a fully-armored knight more or less impervious to attack. With a weapon such as a sword, the only way to overcome full plate armour would be to strike at exposed portions of the armor, namely the armpit, neck, and the groin. If disabled, an enemy could be finished off by having a dagger inserted into the vision slot of their helmet. Knifemen like this were common, but most battles were done with the intention of taking prisoners for ransom, so killing them was considered wasteful. The armpits, neck and groin (and all weak areas) could also be armored with mail. Crushing weapons such as large battle axes and hammers and cudgels were most effective against it. Although well padded, there is only so much trauma a person can take.