Something I came to realise: the competition for grades is not purely about academic ability. It also involves how you handle people.
A familiar situation
A teacher may simply not warm to you. It happens, and it is not always fair.
But look at the timescales: your contact with them lasts a year or two. The grade stays with you for life.
One thing to be clear about
This is not encouragement to use underhand methods to get marks. Not flattery, and not going round the back.
The point is about maintaining a workable relationship with someone who has influence over you for a defined period, even when the two of you are not naturally suited.
Being a bit more even-tempered. A bit more tactful. Not letting personal friction damage something you will carry for a long time.
Why this is a useful exercise
Looking back, it functions as practice in maintaining relationships and defusing difficult situations.
Later in working life you meet the same shape repeatedly: a manager you do not click with, a demanding client, a colleague who has decided about you already. And you still need the work to come out well.
The skill of navigating that is not taught as a subject. But it gets practised, earliest of all, during your school years.