Living on the outskirts of the city, Harry had witnessed things most had not, like the frequent cheating in card games.
Everyone was aware that cheating in those gang-organized card games might lead to terrible consequences, but people still did it.
Because they got blinded by losses.
When people lose to the point of mental collapse, they stop caring about anything, and cheating becomes their only way to break even.
Harry knew of a very simple method, which was to mark the sides and backs of the cards. This method... was almost universally known in the area he lived in.
He didn't dare to mark the backs of the cards so obviously, so he could only slightly dampen the side with a bit of sweat.
If the next player also thought yellow was very important, it meant the color cards were not misleading and pointed to the most likely correct answer, together with other cards forming the clue chain.
