If your manager is assigning unreasonable amounts of work with unrealistic deadlines, and you're taking it on, then you're both contributing to the situation. While it may not be easy to re–set expectations, there are effective ways to keep your workload in check.
How much is too much? Are you willing to work every evening and weekend, and if not what are your limits? The 9–5 job has become a rarity, but that doesn't mean you have to work day, night and weekend. Between the 40 hour and 80 hour work week, we all have a sweet spot. Find yours.
If you have a family, chances are you like to get home in time for dinner. Maybe you'll only work from home two evenings per week instead of five. Take the weekends off with the exception of emergencies, and catch up on Sunday so you don't start the week on Monday feeling behind. Once you know your goals, you can start to experiment.
Before saying yes to each new assignment, ask yourself how important it is, whether it can wait, and if there's someone you can delegate to. If you still end up taking it on, be clear about what you're saying no to – at work, or at home. We all have limited capacity. No one gets more than 24 hours in a day, and we all need to eat and sleep.
You'd be surprised how few people tell their manager when they're overloaded, and how responsive your manager might be. Especially if you're a high performer, the last thing the company wants is for you to burn out and leave. The cost of replacing any employee is high, and the cost of replacing a great employee can mean hiring two or more people to do the job.
A brilliant strategy is to keep a list of everything you're being asked to do and would like to do. Some projects just have to wait until there's more money or resources, and others simply won't get done this year. Work categorized “below the line” is important but not scheduled. If your manager wants to move something above the line, see if you can deprioritize something else. If nothing on the list can't move down, ask for the time, money or resources you need to take on more.
Like a balloon will pop if you keep adding air, realistically there's only so much you can get done with fixed resources. While saying yes may feel right in the moment, your manager will respect you for being realistic and asking for what you need to deliver successfully.