I make noble plans to have my house clean and give the boys a choice after daily chores are done: "You may either stay inside and earn money by helping me or you may go outside and play."
Of course, they choose to play. But soon, one of them comes in with a question like, "May I put some water in this bottle? It already has sand in it, and I want to see what happens when I put water in it too." (They have to ask before they play in water. It's frustrating when all the tennis shoes are soaking wet when we set out to go somewhere.)
I not only comply with the water request, but, to his delight, I add an almost-empty bottle of food coloring. Now, if I were diligent with my household duties, I would send him on his way and get some serious work done. But I just can't. I have to watch him experiment and witness his joy of discovery. Then I have to go to the computer and journal it so I don't ever forget. I learn more than he does when I watch him.