a source familiar with the matter

. @Ken Berry, MD Some people would rather risk the shot than the bug. Generally I'd rather risk the bug than the shot. Also, does the shot even work?

Here's a good example of a sudoku technique I use which I haven't seen discussed. If the highlighted square at the bottom was a 6 or a 9, it would make it so the 6s and 9s in the bottom two squares could be switched around and still solve the puzzle. Because a valid sudoku puzzle has only one solution, the highlighted square must be a 4.