In the lecture, the lecturer mentioned about symmetric and asymmetric designs. I think that symmetric designs are you pretty easy to produce. Such pictures usually appear to be of equal 'weight', balancing on the central fulcrum. Symmetry can also be taught of as a balanced or gradual movement away from the center point. Take for example flowers. Their petals unhold in a circular manner from the center.
Asymmetry is, on the other hand, harder to pull off as we have to consider that the 'weight' of our objects in the picture vary in sizes, shapes etc, thus making the balancing act some what more delicate. This reminds me of those physics based balancing games where you are given boxes of varying sizes and weights and your task is to balance them across some plateform.