For some reason mowing your lawn with a scythe is spectacularly efficient only when the grass is wet (talking about cutting the grass down to essentially ground level, a regular short mowing).
The cutting is done with a razor-sharp edge that advances mostly along its length but somewhat across the grass as well, so it's a slicing like slicing bread.
Two things make it not work very well. 1, the grass simply bends out of the way and so is not cut. 2, the grass cuts partly but sticks on the edge, forming a clump of grass, which stops the slicing action and the blade goes unstable (if it's a long one), generally burying its point very quickly.
When the grass is wet, what happens instead?
One possibility is that wet grass has more momentum and so doesn't bend out of the way when it encounters the blade.
Another is that wet grass is softer or somehow more sliceable.
A third, which I suspect is true, is that the grass is slippery when wet, and doesn't clump on the edge, so the whole length of the edge works on all the blades without their being torn out by the root first.
Various blade styles work differently but all seem to work best when it's wet.
Shorter grass blades don't go unstable in the dry, so are useable, but don't cut very quickly.
This is all talking about regular lawn grass, not standing wheat or anything. Tall grass is another hobby.