A longtime golfer once told me that the difference between a great amateur and a true professional is pretty easy to spot: At the end of a tournament, the duffer hits the 19th hole to relax.

The pro gets some water, changes and heads to the range to hit buckets until closing time.

They compete all day and then get right back out there, slamming hundreds of drives to correct whatever went wrong earlier in the day.

Jim Cramer, the “Mad Money” host, got me thinking about this distinction.

Being in the retirement investing business, I meet people all the time who call themselves investors when, in reality, they act like traders.

Traders don’t own investments. They rent them, short-term. They honestly expect a stock to move one way or another very soon. They trade all day and obsess about trading all night.

When the event they expected comes to pass, they sell. When it doesn’t … they sell anyway. The moment is gone. Move on.

Investors, meanwhile, almost never sell. They own a stock and, when it falls, they buy more of it. Their expectation is to sell someday, down the road, to raise cash for living expenses.

In meantime, assuming all else remains the same, stocks are for holding. “I buy down when I am investing. I cut my losses immediately when I am trading if the reason I am trading the stock doesn’t pan out,” Cramer said on his CNBC show.

It should be obvious why investing works, but I’ll restate it here just in case. Stocks compound your savings well in excess of inflation. Over years of an investing, it’s basically impossible to beat a good, solid stock portfolio.

Stocks beat bonds. They beat gold. They beat cash, of course. Owning a piece of a profitable company means you have rights to corporate cash flows in the form of dividends, and on top of that you have appreciation.

Stocks tend go up in value. Reinvesting dividends supercharges that effect.

Retirement investors find themselves in trouble when they confuse investing with trading. They take a few stock newsletters, start watching the markets on TV and begin to feel like they should trade, too.

It’s a fundamental mistake. Sure, trading is easy. Just about anyone can open an online brokerage account, plunk down a few thousand bucks and go to town.

If you have money to throw away, it’s a hobby of sorts. You end up learning a lot of interesting things about economics and law and how the world works.

If you’re honest about it, though, once you lose that few thousand you should back out of the whole game for good. But that’s not what people do.

Rather, they double down. Inconvenient losses are deemed illogical, chance events. The trader goes back in, intent on making back the loss. Maybe the next trade works out. Instead of chance, now it’s a vindication. They feel emboldened.

On it goes. A decade slips by, perhaps two. One day they wake up and realize that, after fees and compounded losses, their retirement fund is startlingly modest.

Not enough to quit work by any means.

Instead of investing, they traded — and paid the ultimate price for confusing the two.

Many people play golf. Only a few truly compete.

When it comes to retirement investing, knowing the difference is important.