Hard Binairo boards are graded by a strict standard: somewhere on the solve path, pairs, sandwiches, and counting all run dry, and progress requires Binairo's third rule — no two rows are identical, and no two columns are identical. The technique: when a nearly-finished line could complete in two legal ways, check each candidate against the already-completed lines running parallel to it. Any completion that would produce an exact duplicate is illegal, and eliminating it frequently decides several cells at once.
Uniqueness elimination is easy to forget because most boards never need it — which is exactly what makes this tier distinctive. Train yourself to react whenever any line fills completely: scan its parallels, and mark the near-twins one or two cells away. Those are where the rule will bite.
Every hard board is still deduction all the way down — our generator discards any puzzle that would force guessing. If you're stuck, it's provable; re-count, then compare lines. Warm up on the medium tier or today's daily board first.