You manager wants you to agree to the work they ask you to perform, and they want to load you up with work to maximize your efficiency. How one negotiates when you're reaching capacity is professional communications. If one is unable to attain work/life balance that is due to a lack of communication skills, the lack of the ability to explain you're past ordinary capacity, burning your health. Our industry is over run with members over working - that's due to their inability to communicate the are over capacity.