I once saw a man fly through sudokus. I was curious how he could be so good, whats his trick? I asked him because I suck at them. He explained me that its really easy. See these 3x3 blocks? In each block has to be each number one by nine. I told him, that he has to make sure that each row and column also only has one of these numbers.

His mind was blown and than he didnt solve a single sudoku anymore. I was kinda sorry to tell him.