Explanation:

- Sentence Context:

The message warns against becoming too self-satisfied after a success.

- Underlined Word:

"Complacency" refers to being overly content, leading to a lack of awareness about potential risks.

- Option 1: Smug and self-satisfied

This aptly describes "complacency," focusing on unwarranted ease and contentment.

- Option 2: A defensive attitude

This implies being protective, which isn't the meaning of "complacency."

- Option 3: Pride

Although related, pride lacks the aspect of unawareness present in "complacency."

- Option 4: Feeling of superiority

This suggests thinking one is better than others, which isn't intrinsic to "complacency."