What did Stanley think was funny about his mothers letter in the book Holes by Louis Sachar?

In "Holes" by Louis Sachar, Stanley finds it funny that his mother wrote about the family curse, claiming that it was the reason for their bad luck. He chuckles at her belief that they were cursed because of his great-grandfather's mistakes, particularly the way she presented it with such seriousness. This light-hearted perspective contrasts with the gravity of their situation, highlighting Stanley's ability to find humor even amidst adversity.