setAccessible(true) must be called first. Frame the concept in practical terms so you can explain it during interview discussion.
Private methods are inaccessible from outside classes by default. To invoke them using reflection, setAccessible(true) bypasses Java's access control checks, allowing Method.invoke() to be used on private methods. This should be used cautiously, as it breaks encapsulation.
Additional Notes
How can Method.invoke() be used on a private method?