Q & A on portfolio engineering

Why diversify? To avoid total disaster. Staying rich is more important than getting richer.
Why emphasise a top/down approach? Because staying rich is a question of asset allocation, not of stock and bond picking.
Why should portfolios look similar? Because all clients should benefit from the best ideas.
What is risk? Co-variance, not variance if backward-oriented (the answer of the statistician). The possible deplorable consequences of being wrong if forward-oriented (the answer of the economist).