When Larina entered high school she was certain that she would never eat any of the junk food sold in the vending machines. By the end of tenth grade, however, Larina was munching on at least one bag of chips a day. Larina's experience best illustrates

Larina's experience best illustrates overconfidence.

Explanation:

Confidence is an individual's belief that he/she can have faith in something or someone.

Overconfidence is having an excessive confidence, which can often be negative.

In this case, we can see Larina is being overconfident, thinking she will never eat any junk food by the vending machines even though she does in the end.