Let's look at an example. Instinct theory would predict that you have been born with certain abilities and preferences. When a specific behavior is set in motion by the proper stimulus, it will continue in a form common to all individuals with similar genetic structure. You can taste the cookie, and finding that it is sweet, you will be more likely to continue to put it into your mouth. Think of a newborn infant.
Infants seem to be born with a preference for sweet tasting things.
They will suck more actively and not reject a sweet tasting substance, while a bitter or sour substance might cause a disgusted look and mouth movements designed to remove the substance from the infant's mouth. There also appear to be human preferences for fat, another highly nutritious substance and for salt, which contains chemicals essential for many body processes. A sociobiologist might extend this reference and focus on the adaptiveness of this preference. This will ensure our survival as individuals, and the genes which gave us these preferences will be passed on to our children because we will live long enough to reproduce. A drive theorist might focus on your current state of deprivation.