Piaget’s reliance on a verbal explanation of events is a major weakness in his theory. As noted in Chapter 26 on infant cognition, the nature of the task used to investigate how children think can influence the results. For example, compare two seriation tasks: ordering sticks according to length and stacking measuring cups inside of one another. For the sticks, children use trial and error, and cannot focus on two things at once—length of stick and its relationship to what is before and after it. Thus they tend to “complete” the task incorrectly. For the cups, there is only one correct solution. The task tells them when they are wrong, and encourages children to “reverse” the results of incorrect trials—if not in their minds then with their hands. Children successfully seriate the cups because the task provides “error information”—that is, the big cup cannot fit into the little cup. Seriating sticks does not provide that kind of feedback.