Not really related to what I said but I'll bite. Let me try phrasing it in a different way, if someone asked you to, in addition to doing your own job, do someone elses, but instead of paying you for that additional work said you'd get great "exposure" and a future reward, would you jump at that chance?

I know many people that have because they care, they are hungry, they want to advance, they can do higher level things and want to prove themselves, etc. and the vast majority of them have gotten nothing for their trouble but extra work. We live in a world where working hard is always encouraged and its virtues extolled but rarely rewarded.

Except work is nothing like professional sport. Your example is detached from reality.

It's more like being hired as a plumber and start doing secretary work for your boss for free.

There's a price tag on your services, why would give it out for free for some nebulous chance of getting a promo? Peak stupidity.

How's the boss going to know you can do secretarial stuff if he hired you as a plumber?

You go to the boss and you say you want to become a secretary. You and your boss outline a path with clear road and compensation for the effort.