When Jim Cramer first started out in trading, he didn’t like rules. He believed that either they couldn’t really help, or they would cut his upside and prevent him from making more money.

After getting burned too many times, he learned the value of discipline.

“The rules protect you against your own bad judgment about what’s going on at the companies you own or what’s happening in the market overall,” the “Mad Money” host said.

In order to really make money in the market these days, investors need discipline. Mistakes can cost you in trading, but if you do nothing with your money, you will have a whole lot of nothing to show for it.

Investors frequently ask Cramer what to do with a stock after it has had a hideous decline. His first response is always to ask why they bought the stock in the first place.

One of Cramer’s cardinal rules is to never turn a trade into an investment. If there is one thing he wants investors to take away from “Mad Money,” it is to never confuse these two concepts. That means understanding the purpose of why you are buying a stock.

Sometimes an investor will buy a stock for one reason, and then another reason happens. Then they decide to turn the trade into an investment and buy more as the stock goes down. Or perhaps the reason for the trade never happens, so they end up holding the stock.

“What’s the worst thing that can happen? The answer, of course, is plenty, and almost all of it bad,” Cramer said.

One silly mistake that some investors make is to say “if it weren’t for that darned buy of one stock, I could have been up big.”

It only takes one or two losers to wreck a portfolio. Cramer devotes significantly more time to analyzing the losers than the winners, because the winners tend to take care of themselves.

That is why he recommended that investors take the loss on a stock before it gets hideous.

“Don’t buy into the notion that you can’t sell until it comes back, and then you promise not to do it again. That is how losers think,” Cramer said.

The flipside is true, too. Gains won’t be realized until a stock is actually sold, and many investors are reluctant to sell because they don’t’ want to pay taxes. Gains not taken are losses that will be taken, Cramer said.

The biggest mistake Cramer sees investors make is thinking they are supposed to be fully invested at all times. Heck, some money managers have even told him that they are supposed to have all their money in stocks.

This is complete nonsense!

Having cash on hand when a market correction occurs is the key to protecting a portfolio, Cramer says. Sometimes the market will stink, and there is nothing to do but just sit in cash.

“In fact, one of the chief reasons that I outperformed pretty much every manager in the business during my 14-year run as a professional money manager is that there were substantial blocks of time when I was largely in cash,” Cramer said.

Some of the best stocks in the industry require investors to do nothing. Sometimes they can do nothing for ages, racking up small gains over time.

“I say some of the best stocks require some incubation,” Cramer said.

Ultimately, though, Cramer says the business is not about hope. It is about fundamentals. Investors shouldn’t root for stocks to go higher. They simply need to pick stocks of good companies, and be patient unless something changes dramatically.

Questions for Cramer?
Call Cramer: 1-800-743-CNBC

Want to take a deep dive into Cramer’s world? Hit him up!
Mad Money Twitter – Jim Cramer Twitter – Facebook – Instagram – Vine

Questions, comments, suggestions for the “Mad Money” website? madcap@cnbc.com