Nobody really likes the guy who stays too late at the party. You know the one -- he hangs around until the hosts have to virtually toss him out the door. There's a good lesson here for investors: You need to mark that fine line between reaping all you can from a successful investment and not endangering those gains by getting greedy. So while I'm not saying the party is over for copper companies such as Phelps Dodge (NYSE:PD), I do suggest that investors start thinking about an exit strategy.

For the armchair investor, Phelps Dodge's fourth quarter is a nightmare of charges and unusual expenses that make comparisons very difficult. So here are some of the bottom-line takeaways. First, revenue was up nicely, but that growth was due almost entirely to higher prices for copper and molybdenum. Second, copper production slipped about 8% from last year, at least in part because of problems at the company's Candelaria mine in Chile. Third, earnings from continuing operations were hurt by those production shortfalls and by higher overall production expenses.

It wasn't all bad news, though: The company did pretty well from a cash flow standpoint. Operating cash flow climbed by 12% in the quarter, if you exclude a $200 million contribution for retirement benefits. Likewise, management decided to part with some of its growing cash hoard and announced a $4-per-share special dividend.

While every stock is a commodity in its own right, it's fair to assume that, for the most part, Phelps Dodge shares will share more or less the same fate as copper prices. So where's the copper market heading? Prices have shot up in part because of production shortfalls (like the one Phelps Dodge registered) and concerns over strikes at major producers. That said, while inventories are still very low, they're starting to rise, and production capacity is moving from deficit to surplus.

None of that means copper is doomed to fall, even though management seems to agree with the consensus forecast of about $1.70 per pound for copper for the year, versus a current price of about $2.33. After all, it would only take a strike at Codelco or a production problem at BHP Billiton (NYSE:BHP), and that supply/demand balance would tighten up again. Still, I don't think the odds favor another doubling of the stock within the next year, and investors might ultimately be happier with a more diversified minerals-and-metals play, like BHP, Anglo American (NASDAQ:AAUK), or Rio Tinto (NYSE:RTP).

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Fool contributor Stephen Simpson has no financial interest in any stocks mentioned (that means he's neither long nor short the shares).