Winning, drawing, losing, Oh! winning again.
A game in four parts. Part 1: I establish a crushing advantage. Part 2: I blunder badly and let white back in the game. Part 3: my stupidity only increases, giving white a real advantage. Part 4: white miscalculates and I trade down to a won endgame with a single pawn advantage.
Part 1: I take advantage of white's mistakes in the closed Sicilian opening, culminating in a bad blunder by my opponent, and I establish an unambiguously winning position.
Part 2: We leave off from a position in which black has a crushing advantage - up two pawns and a piece with a dangerous looking attack. We find that advantage dissipated almost entirely in one fell swoop.
Part 3: After getting myself in some difficulties, blundering away that piece, and losing one of those pawns, I'm in a tight spot and struggling to develop my bishop. Some sloppy play lets white gain the initiative, and his knight runs riot.
Finally, Part 4: I've managed to put myself in a bad position, and am waiting for white's rook to come attacking. But.....
So white didn't check the possibilities he had to attack, and mistakenly traded down into a lost endgame. All it takes is one move to swing a game. And then another to swing it back the other way. And then another to swing it yet again. And then a bit of calculating to check you didn't count wrong and lose the pawn race. Luckily, here I got that bit right.