For an adult this is pretty clear, but when does the understanding get to be learned by our children?

So as I have 3 children, ages 6 and 2 times 4, I have stumbled on this issue several times. The kids ask’s me to do something, but as it is explained to the kids they can’t understand why not. As late as today, one of my twins asked me to build stairs with Duplo pieces. She had started well with 5~6 pieces, but she wanted the stairs to be longer. When I tried to explain to her, that we didn’t have more pieces, as I just built a house for there play, she just could not grasp the concept, that it was not possible to build a longer staircase.

So her reaction was to get angry and tear apart what she had built, and leave them on the living room floor and walk away. Which of course populated the next “problem” for her, as I told her she can’t leave the pieces there.

But at what age does the understanding come, that if there is no more pieces to use, you can’t build more?

I have tried to explain this several times, over and over again with many various ways, but they just don’t seem to grasp the concept that there is not an endless supply of the thing at question. So for how long will this explaining continue, before they even start to grasp the concept of limited resources?