- A stall almost always means a missed elimination, not an impossible puzzle
- First check: are all your pencil marks up to date?
- Re-scan for Hidden Singles in every unit — they are the most commonly missed move
- Check for Locked Candidates — these appear often and are easy to miss during fast solving
- If still stuck after all checks, look for Naked or Hidden Pairs
Step 1: Verify Your Candidates
Before applying any new technique, make sure your pencil marks are accurate. An outdated candidate is the most common cause of artificial stalls. For every digit you have placed recently, check that its peers have had that digit removed from their candidates. A single missed elimination can hide the next move entirely.
Step 2: Re-Scan for Hidden Singles
Go through all 27 units one by one. For each unit, check every digit 1–9: how many cells in this unit still have this digit as a candidate? If the answer is one, that is a Hidden Single — place it immediately. This is the most commonly missed move at every difficulty level.
Step 3: Check for Locked Candidates
For each box, look at where each digit's candidates fall. If all candidates for a digit are in one row or one column, you have a locked candidates pattern. Apply the eliminations and see if new singles appear. This step alone resolves most Medium stalls.
Step 4: Look for Pairs
Scan each unit for cells that share the same two candidates. A Naked Pair eliminates those two candidates from other cells in the unit. A Hidden Pair eliminates all other candidates from those two cells. Either elimination often triggers new singles.
Step 5: Take a Break
This sounds trivial but works: step away for 5–10 minutes, then look at the grid fresh. Patterns that were invisible during concentrated solving often become obvious after a short rest. The brain's pattern recognition works differently when you're not staring intently — this is why many solvers finish puzzles in two short sessions rather than one long one.
Step 6: Use the Techniques Library
If all the above fail, you may need a technique you haven't learned yet. The techniques library is organized by difficulty. Find the section matching your puzzle's difficulty and check each technique systematically. The Daily Challenge is great for deliberate practice since the puzzle difficulty is known in advance.