why do eggs hold more weight vertically?

Answer 1

I am not sure it is true.

It sounds reasonable because of the way the load is distributed. The egg can break because of what is called shear. In the horizontal the load has what I would call a longer lever arm. That is, the load is a greater distance from the ends of the egg. In the vertical, the lever arm is shorter. Another way of looking at it is that the load gets support from portions of the egg that are put into compression by the load. In the horizontal position, more of the shell is subject to bending stresses. Brittle material usually does not like bending stresses,

On the other hand, when the egg is vertical, the load is supported by a very small area. this concentration of stress could break the egg.