Cutting onions can be a bother.
Sulfur compounds are released when you slice through them.
They mix with the tears in your eyes to form an acid. More or less.
The acid irritates your eyes even more. You close your eyes. You blink a lot. It only seems to make it worse.
The more tears you make, the more acid there is to hurt your eyes.
The trick is not to blink and to keep your eyes wide open.
So much of life is like that.