On (one's) plate phrase
This phrase refers to tasks, things, or responsibilities that one has to focus their time and energy to deal with.
Can you reduce the number of exercises? Because we've already had a lot on our plate.
I hope the Maths teacher won't assign us more homework as I have enough on my plate.
Sorry, I can't hang out with you guys now because I have plenty on my plate at the moment.
This phrase is often used in the phrase "have enough, a lot, etc. on your plate", which dates back to the 1920s.
Someone who has a strong personality
I know Josh could deal with this problem because he's made of sterner stuff.