Refer to the payoff matrix provided. You and your competitor must decide whether or not to market a new product.
1 point: $400
1 point: Market the new product
1 point: Yes
1 point: Profits are greater (either $100 or $400 versus $0) if I market the new product, regardless of what my competitor does.
1 point: Yes
1 point: Both players marketing the product is a Nash equilibrium because neither side wants to change to not marketing, given what the other side is doing. (In fact, in this case both sides want to market the product regardless of what the other side is doing, so it is a dominant strategy equilibrium as well as a Nash equilibrium.)