If recompense is of the same nature as the deed, then how can a person mend himself on his own? And are a wife's disobedience (nushuz) and children's disrespect (uquq) considered part of this recompense?

Recompense is of the same nature as the deed, but repentance erases sins, and Allah may pardon His servant out of His grace. Everything that befalls a servant is by Allah's decree, for a wisdom and a mercy. The servant must repent, be upright, take the necessary means, and have a good opinion of Allah, and Allah will grant him success.