Concept in stoicism: Only the self is on control. Most other things aren't.

Tricky things though

Some things are partially in your control.

For instance, exams - you can store knowledge but you cant predict perfectly what will appear in the exam.

And of course it may lead to surrender or the illusion of power. Both are bad and non-realism.

Worse of all - LITERALLY FOLLOW IT

When you expect stuff like hobbies (in your control) to overcoem stuff like school (cannot control), or somehow think you can avoid a negative reaction to uncontrollable bad stuff it's bound to be a disaster.