Perhaps it is the sense of achievement the child gets when he sees the blocks standing well balanced. The focus and skill required to make something stand tall with a small base as this, is immense. It might all look trivial to see a three year old put one block on top of the other and make towers. But, in the process what the child may not be realising is that he is actually having a hands- on experience of engineering the techniques of gravity, balance and also a sense of sequencing!