Lacking self-confidence and Unsure

Unsure and lacking self-confidence are semantically related In some cases you can replace term "Unsure" with "Lacking self-confidence", this terms are similar.

Unsure adjective - Not feeling sure about the truth, wisdom, or trustworthiness of someone or something.

Lacking self-confidence and unsure are semantically related in unconfident topic. You can use "Lacking self-confidence" instead an adjective "Unsure".