We're getting to six months since the stock market bottom in early March, ending the worst bear market in 72 years. We're now experiencing a rally of more than 50% off that bottom, which makes it the biggest rally in such a short time in more than 75 years.

What have we learned from these historic experiences? As you decide whether to stick with this rally, if you ve been smart enough or lucky enough to participate in it, let's see if we can gain some wisdom from how we could have optimally handled the bottom in March.

How many of us made the right investment decisions in March at that critical turning point? On the face of it, you'd think that most people made very bad decisions the panic of that horrible bottom only occurred because so many people got scared and sold at just the wrong time.

But that doesn't mean the right decision would have been to put all your money into stocks on that day. Sure, it was right knowing what we know now. But we didn't know then that stocks were about to rally 50%. What we really need to do is go back and try to reconstruct what the optimal thing to do was recognizing that in the heat of things we didn't know what the future would bring.

The first lesson in optimal decision-making under the uncertainty and fear that prevailed last March is to think with a clean mental slate. Investment decisions are inherently forward-looking they are about future outcomes so it makes no difference whether you came to the March panic with big losses or big gains in your portfolio or no portfolio.

If you came in with losses, you were probably so remorseful you had no courage to take any risk at all. If you came in with gains, that means you must have been short the market. It must have been very tempting to let your profits ride. Either way, you missed the rally. So any time you have an investment decision, simply forget about whether you happen to be a winner or happen to be a loser at that moment. It makes no difference to the outcome.

The second lesson is have respect for how little you know. Believe me, nobody knew what was going to happen last March. As it turned out, stocks rallied 50%. They could have just as easily fallen 50% given the dangerous state the world economy was in at that moment.

You probably had an opinion in March about which way it would go. But it was just an opinion, and it would have been the height of arrogance to ignore how many uncertainties and unknowns could have made your opinion wrong.

So that argues for scaling back how much risk you take. The logic is simple. Bet a lot on sure things. Bet a little on long shots. Believe me, back in March, everything was a long shot. So be humble. Admit you don't know everything. Don't bet your whole bankroll.

The third lesson is that volatility can be your friend. Markets are volatile that is, prices move around a lot when there is a lot of uncertainty. That's scary as hell. But you can use it to your advantage.

Here's how. When stocks are extremely volatile, you don't need to put as much money into the market in order to get the same effect. Just think about the 50% rally we've just had. Suppose at the bottom in March you only put half your money into stocks. Now you've gained 25% (that is, 50% on half your money).

Twenty-five percent is a great result for six months in the market . In fact, it's a great result for a whole year considering that the average historical return for stocks is about 10% annually. And you got that great result with only half your money at risk.

Now if stocks had gone down, you would have lost obviously. But you would have only lost half as much.

The second lesson and the third lesson work together beautifully. In March, if you honestly admitted to yourself that you had no idea what was going to happen, you would invest only part of your money. But because stocks were so volatile, you still got a great return!

This is a huge advantage that individual investors have over professional investors. Professionals are judged in comparison to the overall market. If stocks are up 50%, the pro has to be up more than 50% or he's a failure. But you don't have to think that way about your own account. If stocks are up 50% and you are only up 25% only! then celebrate! You just made 25%. That's huge, and it just doesn't matter that someone else made more.

Can we use these lessons to decide what to do now?

Sure. First, forget the past. It doesn't matter whether you participated fully, partly or not at all in this rally.

Second, know what you don't know. We still have no idea where the economy is going. It looks to me like the recession is over, but there's some chance that's wrong. Plenty of people who accurately predicted the recession are saying it's still with us. And even if the recession is over, we don't know how vigorous the recovery will be. So whatever you think you know, it s probably best not to bet the farm.

Third, is volatility still your friend? Yes, but a smaller friend than before. As calm has returned to the markets, we have to expect the moves to get smaller and smaller. So unfortunately, you can't have fifty cents do the work of a dollar like you could last March.

Now there's a fourth lesson, one that's unique to moments of decision that come after large stock market rallies. That is: Don't get greedy.

This rally, more than 50% in less than six months, is nearly without historical precedent as I pointed out in this column three weeks ago . Rallies this good, this fast, just generally don't happen. It doesn't make a lot of sense to bet on things that don't often happen happening twice!

Like most sensible things in life, the sensible approach to this market is obvious enough and fairly boring. Be involved. Take a position, but not a huge position. And don't be greedy.