[![enter image description here](https://i.stack.imgur.com/0yHNE.png)](https://i.stack.imgur.com/0yHNE.png)[![although it may be difficult](https://i.stack.imgur.com/ZecAX.png)](https://i.stack.imgur.com/ZecAX.png)I had an English exam where I had to choose the most appropriate modal verb.
The sentence was like this:

***Although he is an obedient student, he \_\_\_\_ be disobedient at times.***

So, I chose ‘**may**’ by assuming the person has the possibility to be a menace.
However, my English teacher considered it as the least appropriate one and tried to convenience me that the verb ‘**can**’ is the best choice as it reflects the person’s ability rather than possibility.

Therefore, I was wondering if my teacher's statement is true from both a native’s perspective and a grammarian’s perspective.