Hi this is Coach Jeremy again, I'm going to show you Legal's pseudo-sacrifice which is quite cute if you haven't seen it before. E4, e5, knight to f3, now the whole point of this is to show what happens, when black fails to develop, and how severe that can be early in the game.
So instead of going knight c6 and developing the piece, black goes d6, we develop the bishop to c4, now black makes this unnecessary move h6, white develops a third piece. Now white is ahead in development considerably, three pieces to none because a pawn move is not a developing move. So black makes their first developing move, and it's the most aggressive move they can possibly make, pinning the knight to the queen. So white just goes ahead snaps the e pawn, and exposes their queen to capture.
The reason why this is a pseudo-sacrifice is because a piece that's pinned in front of the queen is not an absolute pin. It would be an absolute pin were the knight in front of the king. But black greedily takes the queen, not expecting bishop takes f7, check. The knight is cutting off d7, so the king only has one move and then, to black's amazement, knight to d5, checkmate with the knight cutting off the escape squares on f6, applying checkmate and the other knight on e5 cutting off the escape square on d7 and protecting the bishop.
And there you have it, mate with three minor pieces after sacrificing the queen. And this is what can happen if you fail to develop and how dangerous it can get early in the game.