It doesn't matter
It doesn't matter (/ɪt dʌzənt mætə/), it's not important (/ɪts nɒt ɪmpɔ:tənt/), is a good answer to many students' questions.
For example, if an elementary students asks about the difference between "Do you have some bananas?" and "Do you have any bananas?", the best answer is "it doesn't matter". There is a difference, but it's only small. However, the rule is difficult to explain. Knowing the rule might not help the student. They need to be in the right level to understand it.