Ask the CEO of any market leader in any industry and he will tell you that the irony of success is that it forces you to keep building on an already prosperous foundation. In other words, you're never quite finished- despite past achievements.
The Microsofts and America Onlines of the world know this all too well. These companies are great examples of the "success curse" in that they have radically redefined the potential of the markets they dominate (perhaps a gross understatement for Microsoft). So much so that officials of these companies know that their respective dominant positions have become the bull's eye of competitors. Hence the constant push to stay out in front, relying on the combined weaponry of innovation and marketing skill to grow market share and revenues.