[eurleif]

I think it's quite convincing once you know the scientific fact that dragging an object requires half the work on wet sand. What's the alternative: that the Egyptians did at some point drag objects on wet sand, but that they didn't know it made things easier? Wouldn't they immediately learn that the first time they tried it, even if they first tried it for a different reason?

[jacquesm]

Maybe all that happened is that they tried picking up their work after some rain had fallen (this does happen, even there) and they found the work to go much easier. Then when it dried up again they found it got harder, so they re-created the conditions artificially.

[junto]

I imagine many discoveries are made in this manner. I.e. accidental. Sometimes it can take centuries though for someone to see something obvious and realise its potential.