How close can you get?

Favourite exercise for the mind has been Sudoku for many, including me. The selected level determines the challenge posed. When I feel adventures I choose the very hard level. I accept defeat with a smile as long as I complete at least 80% of the puzzle. This afternoon I have a new understanding of the expression: how close can you get. I failed on 4 squares with 2 numbers! The mystery being, how did I do that, where did I go wrong?
In real life I had similar experiences, getting very close but not right on the spot, hitting the dingdong.