無理をなさらないでください

The phrase '無理をなさらないでください' is composed of several elements. '無理 (muri)' means 'unreasonableness,' 'impossibility,' or 'strain.' It's formed from '無 (mu),' meaning 'nothing' or 'without,' and '理 (ri),' meaning 'reason' or 'logic.' So, '無理' literally translates to 'without reason' or 'unreasonable.' 'を (o)' is a direct object particle. 'なさらない (nasaranai)' is the negative form of 'なさる (nasaru),' which is an honorific verb for 'to do.' It's a highly polite way of saying 'しない (shinai),' the negative of 'する (suru - to do).' The use of 'なさる' elevates the politeness of the request significantly, showing respect to the person being addressed. 'で (de)' is a particle here functioning to connect the negative verb to the imperative 'ください.' 'ください (kudasai)' is an imperative form of 'くださる (kudasaru),' an honorific verb meaning 'to give' or 'to bestow.' In this context, it functions as a polite request marker, meaning 'please (do not).' Therefore, the phrase literally means something like 'Please, without reason, do not do (it).' More naturally, it conveys the sentiment of 'Please do not do something unreasonable/strenuous (to yourself),' leading to the common translation 'Please don't push yourself too hard.' The construction emphasizes respect and concern for the listener's well-being, making it a very common and polite expression in Japanese culture when advising someone not to overexert themselves.