Twenty? As many as there are companies?
At the highest level of competitive differentiation there are 3 (but it is still hard to get it right).
Technology changes...strategy doesn't. Change happens faster....strategy doesn't.
THE WORLD'S MOST FAMOUS BUSINESS-SCHOOL PROFESSOR IS FED UP WITH CEOS WHO CLAIM THAT THE WORLD CHANGES TOO FAST FOR THEIR COMPANIES TO HAVE A LONG-TERM STRATEGY. IF YOU WANT TO MAKE A DIFFERENCE AS A LEADER, YOU'VE GOT TO MAKE TIME FOR STRATEGY.