Are you referring to the cognitive process, involuntary reflex, emotion, or…?
I know exactly why I ordered the taco I ate for lunch- I chose (from a multitude of options) to patronize the taco shop because it is close to work and I haven’t much time today, I was hungry, and I find tacos both aesthetically pleasing and delicious.
I even went so far as to commemorate the momentous event with a poem, tentatively entitled In Taco Veritas:
O taco, thy spicy heart and wondrous smell
Embraced (appropriately) with crunchy golden shell;
None can spurn thy precious feast!
My mouth a temple, my tongue a priest,
I worship thee, my culinary jewel,
As I transform thy beauty into metabolic fuel.
Copyright 2008, all rights reserved, yadda yadda yadda.
I hope that answers your question.