Sudoku Flow7 Common Sudoku Mistakes and How to Avoid Them
The seven mistakes that ruin most Sudoku games, why each one happens, and the simple habit that prevents it.
Updated 2026-10-04
1. Checking only the row
You see that a row needs a 5 and place it, but its column or its box already has a 5.
How to avoid it: before every placement, check all three units of the cell: its row, its column and its 3×3 box.
2. Guessing when stuck
When no move is obvious, it is tempting to try a digit and see. A wrong guess can take many moves to show itself, and by then it is hard to undo.
How to avoid it: a well-made Sudoku never needs a guess. Look for a cell with one candidate, or a digit with only one possible cell in a row, column or box. If neither exists, it is time for a technique such as a pair.
3. Forgetting to update notes
You place a digit but leave the same digit in the notes of its row, column and box. Later those stale notes suggest moves that are no longer possible.
How to avoid it: every time you place a digit, clear it from the notes in its three units straight away. Many apps, ours included, can do this for you.
4. Writing only some candidates
Noting only the candidates that come to mind makes a cell look nearly solved when it isn't. A missing candidate is invisible, so you never think to check it.
How to avoid it: in each cell you mark, write every candidate or none.
5. Mixing up rows and columns
When your eye moves fast across the grid, it is easy to check a column when you meant a row, especially near the thick box borders.
How to avoid it: trace the cell's row and its column separately. Apps that highlight the row and column of the selected cell remove this error almost entirely.
6. Placing a digit you can't explain
A digit that only feels right is the most common source of a mistake that surfaces twenty moves later.
How to avoid it: place a digit only when you can say why it is forced, for example: the other eight digits are already in this cell's row, column and box.
7. Building on a mistake
Once a wrong digit is on the board, every candidate it rules out is ruled out wrongly, and the errors multiply.
How to avoid it: when something becomes impossible, stop and find the first wrong digit before you go on. Our guide to finding a mistake shows five quick checks.
Practice
Every Find the Mistake puzzle on this site has exactly one wrong digit, and you can play each board right on its page.
