Imam Ibn al-Qayyim (rahimahullah):

What has passed is not remedied by grief and sadness, but rather by contentment, gratitude, patience, and faith in divine decree (al-Qadr), along with the servant’s words: “Allah has decreed, and He does what He wills. (Qaddarallahu wa ma sha’a fa‘ala)”

Likewise, what will come in the future is not prevented by worry and stress. Rather, if he has a means to avert it, he should not be negligent in doing so. But if he has no means to avert it, he should not despair over it, but rather face it with patience, prepare himself appropriately for it, take the necessary measures, and equip himself with the proper provisions. He should shield himself with a strong fort of tawhid, reliance on Allāh, and humbling himself before the Lord, submitting to Him and being content with Him as the Lord in all matters.

Source: Zād al-Ma‘ād (2/327)