Why bodies with different mass reach ground at same time?

Do you ever wonder why bodies with different mass falls at same rate?

From our school days we learn that no matter what the mass is any number of bodies thrown from the same height will reach the ground at the same time. Do we really understand the physics involved behind this?

Watch the video below to know the physical and mathematical explanation for this.

https://youtu.be/w2Sa-MlI2kU