الْكَيِّسُ مَنْ دَانَ نَفْسَهُ وَعَمِلَ لِمَا بَعْدَ الْمَوْتِ، وَالْعَاجِزُ مَنْ أَتْبَعَ نَفْسَهُ هَوَاهَا وَتَمَنَّى عَلَى اللَّهِ
Translation: The truly prudent person holds himself to account and acts for what comes after death; the ineffectual person follows his desires and merely entertains wishes about Allah.
Source: Tirmidhi and Ibn Majah.
الْكَيِّسُ means the discerning, prudent person. دَانَ نَفْسَهُ includes restraining and taking stock of oneself. وَعَمِلَ means “and acted,” showing that intention should lead to conduct.
In contrast, الْعَاجِزُ here refers to someone who allows desire to dominate and neglects real responsibility. The warning is not a condemnation of bodily weakness or illness.