This being Missouri, Bench presumably said, "Show me."

Voila! A loaf of bread instantly sliced to symmetrical perfection!

"Frank Bench's bakery increased its bread sales by 2,000 percent in two weeks," Rohwedder's son, who was 13 years old in 1928, told the Chillicothe Constitution-Tribune in a 2003 interview. Before long, Rohwedder had a backlog of orders; his slicers helped put the wonder in Wonder Bread.

Now, from Cupertino, Calif., comes Apple's iPhone, the latest in a line of marvels vying to be the greatest thing since you-know-what. Seldom has any product been so hyped or anticipated. But history suggests that some of the most successful innovations seemed to come out of nowhere - to fulfill a desire that the public didn't even know it had. (Why, before sliced bread, many people had no idea they wanted a toaster.)

What does it take to make the proverbial "new new thing" become an object of desire? What separates contenders from pretenders? Some products soar with mass appeal, while others meander off to Nicheville, like the Segway or Roomba.

Ubiquity isn't the test. Quantity doesn't mean quality. A large demographic is dazzled by Happy Meals. And was the success of Microsoft's Windows a matter of brilliant design, or market power? And mere fads - think Tickle Me Elmo - don't measure up.

Innovations ultimately succeed or fail on their merits. Analysts say the common denominator is a harmonious blend of form, function and value.

And then there is what has been called "the ooh factor."

"Look at the Nintendo Wii," said Chris Crotty, a Santa Clara, Calif.-based consumer electronics analyst with iSuppli. Literally a game changer, the Wii dazzles consumers with its ability to wield a kind of magic wand for video games.

"It's an incredibly hot product because its simplicity appeals to a broad group of users."

A self-described "gadget guy," Crotty became a Palm fan with the original Palm Pilot, and now uses Palm's Treo.

"When you think of the Palm Pilot, the original, they really defined the PDA."

The Pilot, Crotty noted, even popularized the term PDA, short hand for "personal digital assistant." The earlier, less successful devices were called "electronic organizers."

Quality, not hype, enabled Apple's iPod to come to dominate the MP3 market, he said.

"Others existed, but Apple really came in with best-in-class," Crotty said. "It really married function and design in an elegant solution that most consumers preferred." And with iTunes, it revolutionized the music business. Apple delivered not just a device, but "the ecosystem."

Timing is important - to catch a wave, if not create one. This is another Apple specialty, Crotty said. The company is patient and methodical about how it invades new markets.

Even so, "no one can predict a fad or even a fashion," said Sam Vikram, an Israeli author who writes frequently on technology and trends. "The popularity of consumer goods products depends on numerous factors and often they reflect a trend rather than create or set one."