"Egypt rejoiced when they went" (Psalms 105:38). Said Rabbi Berechia:
This is comparable to a fat man who is riding on a donkey.
The donkey longs: "O when will he get off me"; and the man longs: "O
when will I get off the donkey." As soon as he gets off, the man is happy
and the donkey is happy. Still I do not know: who is the happier?
So, too, when the Jews were in Egypt, and the plagues were befalling the
Egyptians, the Egyptians were longing: "O when will the Jews get out!"
And the Jews were longing: "O when will G-d redeem us!" As soon as
they went out and were redeemed, these were happy and these were happy. Still, I
did not know: which was the happier? Until King David came and said: "Egypt
rejoiced when they went..."