There's a reason we warn readers not to pay too much attention to analyst estimates for future growth. Sometimes the dreams don't come true, and when reality rears its head, it can be ugly with a capital Yuck.

Take big truck maker, and maker of big trucks, Navistar International (NYSE:NAV). This morning's second-quarter earnings report looks respectable. Earnings of $0.54 per share reversed a hefty loss for the prior year and reached the high end of management's guidance. The 21% revenue growth even exceeded the street's expectations.

But Wall Street wisdom predicted more -- up to 30% more. To rub salt in the second-quarter wound, the firm issued guidance for the next quarter of $0.60-$0.70 per share, well below the $0.76 to $1.20 that the same industry soothsayers were seeing in their crystal balls. The news sent investors screaming for the exits, spanking the stock 14% in early trading.

Despite cutthroat competition from the likes of DaimlerChrysler (NYSE:DCX), Ford (NYSE:F), GM (NYSE:GM), and Paccar (NASDAQ:PCAR), Navistar has been in the midst of a decent turnaround. That doesn't mean that it's all cake and party hats in Warrenville, Ill. Higher material costs, along with assorted other manufacturing hurdles, meant that the firm couldn't deliver the expanding gross margin that everyone hoped for.

All right, so Navistar didn't quite get the job done. Still, you can't help but wonder if investors don't deserve a bit of today's reckoning. Sure, it's tempting to believe that your favorite firm will always under-promise and overpay, but that's an especially dangerous game in low-margin, cyclical industries. When third-party earnings estimates vary greatly from the company line, Fools tread carefully, and bid accordingly.

If you dig the big rigs, share your passion for engine grease in the Fool's Buying and Maintaining a Car board.

Fool contributor Seth Jayson thinks Navistar could jump-start bus sales by licensing Otto Man from The Simpsons. He owns no company mentioned. View his Fool profile here.