What Makes You Think You Can't Handle It?
Have you ever surprised yourself after a stressful time or situation in your life?
How did you handle it?
So what makes you think you cannot handle it this time around?
The only way to increase your muscle mass is to lift heavier, same with your stress tolerance - test your limits. Not saying not to take breaks, etc. but we never know how much we can do / handle / accomplish until we push ourselves.
Muscle is built by breaking down muscle tissue, mindset is built by adopting a positive attitude towards challenges. With an abundance mindset, as our responsibilities increase, so does our tolerance. Keep your eyes on the end goal and you will see the challenge decrease in levels of scariness.
While still respecting your limits, do not limit how much you take on by thinking you cannot manage, find efficiencies and just try - see how far you can go with the goal.