impromptu Seth Godin blog:<p>Business ideas are like ice cubes in a tray. You have a lot of different slots, you pour water into each one, and then you put it away in the freezer. A little while later you come back, and some of the ice cubes are frozen all the way through. Some are still full of water. You get both kinds of cubes. The real trick is telling the difference between them. On the surface they both look like fully frozen ice cubes. But the improperly frozen ones have bubbles that move, and the fully frozen ones have bubbles that stay still. You can't tell just by looking at them. The only way to tell the difference is to shake the tray.<p>Shake the tray. Find the fully frozen cubes.