If all our wealth is concentrated in a single pillar, and something bad happens to that pillar, we stand to lose everything.
It follows that our overall objective should be to collect as many different pillars as possible.
The point in having multiple pillars is to provide diversification. Diversification is a risk reduction mechanism which is best summarized by the expression—don’t put all your eggs in one basket.
As an example: if all your wealth is in your private practice (you have no savings elsewhere), and the business fails, say due to a malpractice judgment, you would have no wealth left. In contrast, by spreading your wealth over multiple pillars (or assets), if one suffers a large loss, the other pillars are still there to support your financial needs.