Sam Wan comments that “the coolest toys are the ones that give users the freedom to find their own uses for that toy.”
In Vygotsky’s Mind in Society, he notes that “play is the realm of spontaneity and freedom.” However, in his studies of imaginative play in children, he observes that children will subordinate their own wants to the greater pleasure of following the rules. He concludes that “the essential attribute of play is a rule that has become a desire.”
Rules provide freedom. The really fun toys give you just enough constraints to inspire creativity and make it easy to create great stuff.