The engine said it is a draw I said no

Ready to say "No" to the engine?

Position.1 – The Impenetrable Pawn Chain

I came across this interesting position while browsing the Chess.com forum (Why was I on Chess.com? Let me clarify: I'm not a spy sent by Chess.com to Lichess. I'm just an ordinary player. My Chess.com account was lost during my last computer update – can't recover it). It might be a composed study. Stockfish 18, at depth 15, evaluated it as -3.2, a winning advantage for Black. But hidden within the position is a secret that even the engine wouldn't discover: 1.Ba4+!! a forced bishop sacrifice. Black has no reason to accept it, but if he does, White creates an unbreakable, locked pawn chain. Anyone with eyes can see it's a draw, because Black has absolutely no way to checkmate White's king. So what was Stockfish thinking? That greedy engine only cares about material advantage. It only saw that White lost a bishop and is down so much material – must be losing.

Position.2 – Too Greedy to Dare Sacrifice the Queen

This composition comes from ARVES. It's extremely difficult, and the truly mind-blowing part is the solution: 1.Qc8! 2.Bc7!! – yes, you read that right. White sacrifices the queen on the second move. What's even stranger is that before a human pointed out Bc7, the engine thought the position was equal. Then, when the human suggested this brilliant move, the evaluation bar shot up like crazy, all the way to #11 – forced checkmate. Without human intuition to guide it, the engine's internal algorithm "gave up" on this queen-sacrifice line early in the calculation. Because its evaluation function sees a lost queen as a huge material loss, not worth wasting computational resources on that branch

Position.3 A non-existent chessboard

"This position is illegal," the original poster commented. But a composed study doesn't need to appear in a real game. As long as it stumps the engine, it's a good study. When the game reached move three, Black played 3...f3, and suddenly the engine made it clear that this was no simple puzzle – its evaluation bar started climbing dramatically

Why Do Engines "Crash"?

1. Stockfish's core algorithm is based on Alpha-Beta search. To reach deep search depths with limited computing power, the engine uses various "pruning" strategies. Unpromising moves are cut directly from the search tree. This design is efficient in the vast majority of positions, but when faced with complex compositions, the engine may prematurely discard winning paths

2. Null Move Pruning is a classic heuristic: if a side can maintain an advantage even by "doing nothing," then the current branch isn't worth exploring further. But Zugzwang positions are exactly the counterexample to this logic. This strategy breaks down when encountering zugzwang

3. The NNUE technology introduced in Stockfish 18 is essentially a fit based on massive game data. It performs brilliantly in normal games and standard openings, but its training data contains almost no bizarre, unconventional positions. So when it encounters strange compositions, the evaluation bar may jump up and down erratically

4. Engines prioritize material advantage and direct checkmate threats. For moves that require huge material sacrifices in exchange for long-term tactical compensation – such as sacrificing a queen to create doubled pawns or to expand an attack – the engine instinctively avoids them

   Relevant Links (URL)

   https://www.chess.com/forum/view/more-puzzles/this-position-breaks-stockfish-both-12-and-14
   https://www.chess.com/forum/view/general/why-cant-stockfish-solve-this
   https://www.chess.com/forum/view/more-puzzles/stockfish-at-depth-40-fails-to-solve-this-puzzle-can-you-do-it
   https://www.chess.com/forum/view/general/why-dont-engines-understand-fortresses