Saying No is something we must learn. Sometimes it is necessary to say it...and to receive it too.
I used to work with a manager (now I am a manager too😀), who complained about overload of tasks and that clients did not let him "work". We used to have meetings with the rest of the work team and in one occasion we made a dynamic about the things that any of them believed that one of us should improve or change. My answer was: Learn to say NO. His work overload was not such, but he had the time he had to dedicate to his activities to "attend" some clients in needs or services that were in charge of other people in the team. His sense of service was admirable, but poorly managed and detracted from his efficiency in the performance of his role.