The book says: if you’re shooting for second place, your strategy is determined by the leader. Leverage the leader’s strength into a weakness. Don’t try to be better than the leader, try to be different. E.g. Pepsi marketed itself as a “choice for the new generation” when faced with Coca-cola’s “old and established” brand.
My comment: sounds correct although doesn’t apply to those who do have ambitions to overtake the leader in exactly the same category (which happens e.g. Excel took over Lotus 1-2-3 by being a better spreadsheet, not a different spreadsheet).
See also Eric’s take