To "undermine" confidence means to:

To "undermine" confidence is to weaken or damage it. The term "undermine" inherently suggests a gradual erosion or sabotage of something's stability or strength. When applied to confidence, it conveys the idea of causing doubts or creating conditions that lead to insecurity, thus diminishing a person's or group's belief in their abilities or decisions. This can happen through negative reinforcement, criticism, or even self-doubt, ultimately leading to a decline in total confidence.

The other options imply positive actions that reinforce or support confidence rather than diminish it. Therefore, they do not align with the meaning of "undermine," showcasing that the correct choice accurately reflects the intended action of weakening confidence.