This is where the final stage begins. You need to start making guesses to
arrive at the complete solution.
What I do is look for a mini-grid with two squares not filled in. Usually,
there are two numbers left, both of which are the same, and then work from
there.
Guessing that one number goes into a square means it will not go into any
other square in the mini-grid, row, or column. If you guess it right, the
solution reveals itself.
In some Sudoku puzzles, I reach the final stage with three or four squares
not filled in some mini-grids. This makes the guessing game more tedious but
challenging.
With a bit of practice, a quick glance reveals the solution, and the
fulfillment at cracking another Sudoku puzzle fills you with relief.
By this time, close to an hour had passed and your subway
ride is over. Your mind, refreshed and feeling like a winner, is ready to
tackle less serious matters at the office.