Thanks for fixing my broken english.

There is actually several quotes expressing the same idea in different Terry Pratchett's book. Everyone of them much better than what I could remember. I dug these two ones:

In Wyrd Sisters you have (Granny Weatherwas speaking): “The reward you get for digging holes is a bigger shovel.”

And another one from "Carpe Jugulum" that I like even better (also Granny Weatherwax speaking): "The reward for toil had been more toil. If you dug the best ditches, they gave you a bigger shovel."