Every square can be reasoned out. Every grid opens on a highlighted cell that's proven safe — dig it first to reveal your opening. From there the grid is proved solvable by deduction alone before it ships — so if you're guessing, there's a step you haven't found yet. Which is why one mine ends it: a mine is never bad luck here, only a step you missed. Tap to dig, long-press (or right-click) to flag. One grid a day, the same grid for everyone, no rerolls.