"na asat AsIt" -- "Non-being was not"
"na sat AsIt" -- "Nor being was then"
A poignant verse from the Rg Veda, and one of the most interesting sanskrit grammatical concepts - the idea of balance. Everything has an opposite. If there is dharma, there is adharma (not dharma). The devas had the asuras, who, from what I recollect about ancient scriptures, were not necessarily evil, just their counterbalance. Sanskrit philosophers understood Newton's third law well: for each action there must be an equal and opposite reaction.
Which brings us full circle: if there is being, there is not being, which is altogether different from lack of existence. Raising the question...what was there before being and the opposite of being (non-being)?
This is probably where the concept of zero also comes from - this philosophy of balance. If there are numbers, what is the non-number?