What to try when a Sudoku puzzle feels stuck

First separate a technique gap from a transcription error. Recompute candidates for one row, column and box directly from placed digits; if those disagree with your notes, rebuild the affected region before searching for a new pattern. A unique solution does not guarantee that singles and pairs are enough. If the puzzle promises a logic-only path, escalate in order to locked candidates, hidden pairs and larger patterns while recording the exact elimination each pattern justifies. A contradiction after an assumption is backtracking, not a logical placement.