One ingredient that is often considered a "secret" for tasty apple pie is a combination of spices. Cinnamon is a classic choice that pairs well with apples and adds warmth and depth to the pie's flavor. Other spices that can be added to complement the apples include nutmeg, allspice, and cloves. Additionally, some people like to add a touch of lemon zest or a squeeze of lemon juice to brighten the flavor of the apples. Ultimately, the choice of ingredients will depend on personal taste preferences and the desired flavor profile of the apple pie.