Investors should invest on what they know. The biggest mistake is to invest on what they don't know.

America's downgrade may serve as a wakeup call for its policymakers. It is an unambiguous and loud signal of the country's eroding economic strength and global standing. It renders urgent the need to regain the initiative through better economic policymaking and more coherent governance.

[When] the market is trying to get to terms with, first, lower global growth, particularly out of emerging markets and China. And, second, the market is worried the central banks have run out of ammunition. So put these two things together, and then investors are repricing the market lower.

Most people are under exposed to global assets, including foreign stocks, bonds and currencies.

Once you start moving [market] lower, then you trigger of all sorts of things. You trigger people who have to sell because they're over-levered. So they sell their winners and their losers. They're just trying to raise cash. So, what you then get is spreading malaise throughout the global markets.

It is hard to imagine that, having downgraded the US, S & P will not follow suit on at least one of the other members of the dwindling club of sovereign AAAs. If this were to materialise and involve a country like France, for example, it could complicate the already fragile efforts by Europe to rescue countries in its periphery.

Today's reports confirm that, unfortunately, post-crisis America is still not back to its good economic self.

As a whole, investors should welcome attempts to safeguard the integrity of markets. You need very clear rules applied to markets.

The theory is that if you take interest rates negative, people are going to say, That's a silly game! I'm not going to lend my money to governments who want me to pay them. I am going to go into the stock market where I can get positive returns!

We normally think if you're going to lend someone money, you should get some reward for doing this. In Europe, it's a tax!

The world changes! So we're in a situation today where the only policymakers that have flexibility are central banks. But they don't have the instruments! So they've had to experiment, and the more you experiment, the more uncertainty and the higher the risk of collateral damage.

If you happen to be the only one with negative interest rates, you also weaken your currency, which means you make your exports more competitive.

As we spend more, and as companies are pushed to invest, they say, Hey wait a minute! There's more demand in the system. Let's invest more.

I remember when I was growing up, you would go to a bank to open a deposit, and they'd give you a toaster. A free toaster. These days, if you're a company, and you go to a bank, they could easily turn you away! They don't want your deposits anymore.

Investors should be cautiously positioned as the global economy and markets face major uncertainties. The downgrade will be a further headwind to growth and job creation in the U.S.