Synergy, in general, may be defined as two or more agents working together to produce a result not obtainable by any of the agents independently (Wikipedia).
Or put another way:
Sugar + Butter + Cream + Heat =
Salted Caramel Sauce
adapted from Smittenkitchen.com
1 cup sugar
6 tablespoons salted butter at room temperature
1/2 cup plus 2 tablespoons heavy cream, at room temperature
Place sugar in a saucepan, at least 2 or 3 quart size. Turn heat to medium. Start whisking just when the sugar begins to melt. At first the sugar will clump up and be sandy and gritty and you will think you have made a terrible mistake. You haven't. Keep whisking. Continue whisking until sugar is completely melted and a dark copper color, like the picture above.
Right when the melted sugar is a beautiful deep copper color, add the butter, stir quickly to incorporate, and turn off the heat. Remove the pan from the heat and quickly add the cream. Be careful as the caramel will bubble vigorously. Continue to whisk until the caramel is completely smooth.
Use right away, or refrigerate in glass jars. It will keep several weeks, or longer, depending on your level of self control.
As the caramel cools it will thicken considerably. A 20 or 30 second blast in the microwave will loosen it up.
Serve with: crepes, apples, pears, strawberries, pretzels, fingers, spoons, angel food cake, ice cream, hot chocolate (eat your heart out Starbucks), etc.