The phrase "have second thoughts" typically signifies a change of opinion or reluctance to proceed with something previously decided upon. Antonyms for this phrase can include being confident, decisive, unwavering, resolute, and certain. Alternative phrases to express these opposing sentiments might include "feel sure," "commit to," "be adamant," or "have no doubts." Ultimately, the antonyms for "have second thoughts" suggest a level of conviction and faith in one's actions or decisions, as opposed to hesitation or wavering. By embodying these opposing sentiments, one can articulate a more confident and assured approach to everyday life.