ʿUjb: Being pleased with yourself
Al-Ghazali treated self-satisfaction as an illness of the heart. Someone sure of their own decency quietly stops checking, so their faults sit there unexamined and comfortable. They can list another person's failings fast and accurately, while honestly believing they carry nothing that size themselves.
Muḥāsaba: Calling yourself to account
Al-Ghazali describes sitting down at the end of the day and going over your own conduct, the way a shopkeeper goes over the books. The habit changes who you measure yourself against: not the person in front of you, but yourself yesterday, which is a much harder comparison to win. People who keep it up tend to lose their appetite for other people's failings, since their own list keeps them busy.
The believer is a mirror to the believer: another person shows you yourself
A saying of the Prophet, which al-Ghazali turned into a method. The fault that irritates you most in someone else is usually one you know well from the inside, which is why it registers so fast. The irritation becomes information: the sharper your reaction, the more likely something of the same shape is sitting in you.
Sitr: Covering someone's fault
The Prophet said that whoever hides another person's fault will find their own hidden. Announcing a fault, even accurately, mostly serves the announcer, putting them on higher ground and the other person on the spot. Keeping it quiet costs you that small pleasure, and it leaves the other person still able to hear you later, if something needs saying.
Naṣīḥa: Wanting good for someone and saying so
The Prophet said religion is sincere goodwill. The whole difference sits in what you want for the person while you speak: their good, or the satisfaction of being the one who was right. Words that come from wanting someone well can be taken in, and the same words aimed at proving a point make people defend themselves instead.