There is this C,E of a multi national company whos office is located on the 15th floor of a 20 storry buildng?

when ever he comes to office if alone at lift ,he stops at the 10th floor and uses the stair case to finish up the remainig five, but with other staff in the lift he goes straight to his office. My question is why is he not going straight to his office when alone in the lift?
There is this C,E of a multi national company whos office is located on the 15th floor of a 20 storry buildng?
Is he a midget/dwarf/person of restricted height who can't reach the 15 button by himself.
Reply:It's his way of keeping fit but he doesn't want anyone else to know that he does it.