De Boer's side have now lost their first three fixtures by an aggregate 6-0 scoreline, and the Dutchman hopes that the "very hard lesson" will help them to become a better side after the upcoming international break.
"We have to show some balls from the first second of the game," he told BBC Sport. "It wasn't until after we were 2-0 down, that we showed we really can play.
"It was not because of the quality of Swansea that we lost. We made two mistakes in the first half, they had two half-chances and scored both times.
"It is a very hard lesson for us. If we do not show balls or courage then you get punished. In second half you saw a different Palace who creates chance and with a bit of luck you make one of those. It just wasn't the day for us.
"Hopefully you will see a different Palace after international window."
Palace's first encounter after the break is a trip to Burnley.