There are 3 way you can be better at aiming with a mouse:

Disable acceleration (enhanced pointer precision)

Lower your sensitivity

Use a lighter mouse

Past that, it’s practice, practice and more practice. If you only recently moved over to M+KB, you haven’t developed the muscle memory. Start with games that just require you to click on things, like Civ games or Stardew Valley, and games that don’t require rapid movements, like Portal.

AFAIR it follows E = mc^2, so even 5 grams will give you quite a boom.

Well, a black hole with the mass of an A4 page is gonna evaporate almost instantly, turning all of that mass into energy. Those 5 grams will give you about a 100 kT explosion.