"Night in broad daylight"

A solar eclipse develops when the moon takes position between the sun and the Earth. This implies that the moon is blocking the sun more and more during the birth of a solar eclipse. In a partial eclipse, still enough sunlight gets through to Earth so that we do not notice anything about it. The eclipse takes form gradually. Our eyes get the chance to adapt themselves to the new situation.
During a total solar eclipse, this is entirely different. In the beginning, one does not notice many differences as well. But as the moon blocks more and more sunlight, it will get more and more dark.
When the moon is covering the sun entirely, it suddenly gets very dark. This happens a bit to fast for the human eye to be able to adapt itself. So in the very beginning, you will not be able to see a thing. After some ten seconds, your eyes are used to darkness again (as you experience at night), but is still remains obvious that it is very dark.