Former chemistry student here. In chemistry, every single thing you ever do gets multiplied by a ridiculously big number. A few drops of water has 6.02*10^23 molecules in it. So even the tiniest chemical reactions are massive exercises in parallel processing, and measuring in human-scale units means you might miss by a few hexillion in either direction.

Isn't it amazing internal combustion engines...ever work?

I wish doctors would do the same.