Never assume that someone else is keeping your priorities in check. You have to do that yourself. You’re the only one who really knows where you spend your time on, and you’re in the best position to relate them to the bigger goals you are a part of. To be as effective as possible, you’ll have to guard that, as good as you possibly can.
As a leader, you’ll have an added responsibility: the priorities of the people you manage. Never assume they are keeping their own priorities in check. If their actions don’t match up with your expectations, don’t assume that they don’t agree with you. They probably misunderstood you or just forgot what you said. Keep reiterating your main focus. Keep checking in. Never assume.