Give yourself permission to be brief when you need to be brief.
And give yourself permission to be lengthy when you need to be lengthy.
But whatever you do, don’t make the mistake of refusing to give yourself permission to write anything just because you fear being too brief or too lengthy.
It’s better to write too little or too much than to write nothing at all.
“Too little” can be used as a foundation for more.
“Too much” can be edited and sized down to what is essential.
Nothing? Well, you can do nothing with nothing.
At least write something. It may not be the end-all/be-all, but you can always build on something.