"保持自信"的英文表达是 "keep one's confidence" 或 "maintain one's confidence"。这个表达的来源可能源自于人们在各种情况下希望保持自信心，以便能够应对挑战、克服困难、实现目标等。
下面是一些例句：
It's important to keep your confidence even when things get tough. (即使遇到困难时，保持自信也很重要。)
She managed to maintain her confidence despite the setbacks. (她在遭受挫折后还是保持了自信。)
He always keeps his confidence up by reminding himself of his past successes. (他总是通过提醒自己过去的成功来保持自信。)