Advice from the value investing expert Jeremy Grantham to the shocked and scared investors of today is: Follow your fear. Or, as he puts it, invest when you're terrified. Grantham, who predicted the long-term correction the stock markets would take over the past decade-says now is the time to get back into the market, just as it was time to leave the party during the tech boom.

According to him it was psychologically painful in 1999 to give up making money on the way up and expose yourself to the career risk that comes with looking like an old fuddy-duddy,". He adds that it's seen as equally perverse to jump back in with both feet, as he advocates now. What may be hardest for investors, he says, is to part with dearly held cash, especially since credit markets are so dry. But part with it investors must, because those with too much cash will miss a huge part of any coming market rally.

"Life is simple: If you invest too much too soon, you will regret it," he says. "On the other hand, if you invest too little after talking about handsome potential returns, and the market rallies, you deserve to be shot."

Although it's very hard for retail-level investors to deal with that much fear. "You should always [overcome your fear] in a way where you have a real deep confidence that, even though it's risky, it's the right thing to do,"

Most investors sell when everyone else sells and buy when everyone else buys, ensuring losses.

Let's talk about reinvesting when you're terrified. What do you make of this idea of reinvesting when you're terrified? It seems counterintuitive, but maybe that's why it's a good idea. The thought of doing anything when you're terrified is a terrifying thought.

The professional investors have known it for long and more and more average investors are beginning to appreciate that the process is critical to long-term success. You should overcome your fear. But you should always do so in a way where you have a real, deep confidence that even though it's risky, it's the right thing to do. It's not a guaranteed outcome, but it's a prudent behavior as opposed to simply closing your eyes and jumping off the cliff.

When you're reinvesting when you're terrified, if you have foresight, you'll actually be sticking with your plan that you had all along that you're now scared to execute and in the process you miss out on great investing opportunities. Overcoming your fear when you have a plan and a process, that just makes all the sense in the world. Because rationally, technically and value wise you could know it's a good time to invest. But you just don't feel good about it. That's different than just plunging in the stock market because you think it's at the bottom of a market.

It's contrary to most people's nature to invest when they are terrified. I believe that the best time to buy is when everybody else is selling. And the best time to sell is when everybody else is buying, as a general rule. And we've looked at studies that show that the individual investors in particular are, over the long term, not very good at timing markets, and tend to be very bullish when the market is very bullish, and invest additional amounts, near peaks. And as the markets decline, they want to sell and limit their risk.

The average investor, I believe, won't buy when he's terrified. Although it's probably sound advice. So it's hard to be confident when the environment is something you haven't experienced before. So, for the average investor, what they're seeing right now is so outside of anything they were thinking would happen two years ago, that they're stunned.

What is your time horizon? What are you goals? And, you know, what kinds of risk do you want to take to get there? And I think, for most of us, it really just helps to have that third-party review from experts and discussion to help us come up with a plan in the first place, and then stay focused.

Once you have some clarity in your mind and a plan to invest, you should stick to your guns and don't be in a freeze mode because of fear. Best stock market investing opportunities come in times high turmoil and financial instability. We are passing through one of the worst global financial crisis and according to some experts this might be a once in a life time investing opportunity.