When I casually think of an explosion I think of a rapidly expanding sphere of gases. It turns out this is rarely the case. An explosion propagates from the point of detonation along a (typically expanding) "front". Because the pressure at the front is much greater than both ahead and behind it the gases produced, which are behind the front, expand in a direction away from the front. This video from Ry demonstrates that. The exploding targets are 7" x 7" x 1.375". The gases expand into the axis parallel to the 1.375" dimension. Until this video we did not realize this.

Whatever shape of the explosive and whereever the point(s) of detonation are affects the directions of the explosion. This is used to great effect in the Rocket Propelled Grenade (RPG) which can, with a rather small amount of explosives, penetrate over 30 inches of renenforced concrete, or a foot of steel.