There needs to be an explanation, so here it is, modern tank armor is insanely hard to break through with brute force, as such many modern antitank weapons use special tricks to defeat said armor, for instance, there are weapons with an armor peircing point followed up by a shaped charge explosive designed to go off very shortly after impact. These methods are designed to penetrate hardened steel, not wood and not cardboard, and like trying to use a metal cutting saw on wood, the penetrating point tends to get stuck in the comparatively soft layers of fibrous material, which causes the relatively small explosive charge to blast more or less harmlessly against cardboard and intact metal armor. Other methods used have included covering tanks almost entirely in lengths of hanging chain, sandbags, etc, anything that can prevent penetration of the tanks armor or cause weapon systems to fail.