It's difficult because taking for granted and relying on someone being predictable are very close. Is assuming that someone will behave the same way in the same situation all the time predictability or taking them for granted?
Being unpredictable isn't usually good for a relationship. It makes someone difficult to approach, sometimes thinking silence is the best bet - which leads to bottling things up or being too formal when communicating. It's a bit of a joke relationship if you have to start with a diplomatic preface ALL the time!
The difference to me is about exchange. It isn't difficult to show gratitude in some way if relying on someone's predictability. Even a heartfelt "thank you" is better than nothing; or a willingness to have their own predictability relied on; or an "ok, then," if you don't feel like doing something normally expected and you say, "excuse me this time but I don't feel like doing (whatever)". If someone shows a genuine interest in their partner without being too intrusive the issue doesn't often arise.
But if it starts to annoy you unbottle it and tell the person they're taking you for granted and you don't like it. Depending on the response you'll soon know what the relationship is about.