The problems associated with the decision of whether to lunch at Popeye's, Burger King, Taco Tico, or Little Saigon (a Vietnamese restaurant) illustrate: a. how direct competition affects consumer behavior.
b. how some products and services are competitive substitutes for each other.
c. the strange food tastes of some of us-I mean, Taco Tico?
d. the universal nature of competition. e, that some people just can't make up their minds.

a. how direct competition affects consumer behavior.

Explanation:

The restaurants mentioned in the question are all directly competing with each other to sell food to customers.

Consumers can therefore be spoilt for choice sometimes with where they want to eat at due to this competition and so they will have to come up with some decision making method to decide. This shows that these companies competing with each other imparted consumer behavior.