Oh, Sergio Aguero.
The stars had aligned for him to seal the Premier League title with the ball at his feet on the penalty spot to double Manchester City's advantage. He blew it, the Blues surrendered their lead and the wait to secure a third title in four years goes on after a 2-1 defeat.
When Pep Guardiola made nine changes to the XI that knocked PSG out, expectations that City could box off the league in the next 90 minutes dropped. When they made eight for the FA Cup semi-final, it was a limp performances that saw their Quadruple hopes ended by the same opponents.
Whether the City boss wanted to make a point after being annoyed by criticism for that FA Cup selection or simply didn't want to give too much away to their fellow Champions League finalists, it put a different slant on the game.
Ruben Dias and Ederson were the only two retained, leading to a shape that was heavy at the bottom and the top and light in the middle; Benjamin Mendy stepped forward to help Rodri when he could, and Sterling dropped back in the Bernardo Silva role.
The unusual structure of the team threatened to cause them problems as early as the 13th minute, when Sterling lost the ball close to his own penalty area and was booked for bringing down Timo Werner in a dangerous position as he tried to salvage possession.
As the hosts started to settle though it became apparent that they did not have much to fear from their opponents, Chelsea resembling a team that were trying to bore their way to victory. They were disciplined, they were effective, but with Werner leading the line there was nothing to even remotely trouble Ederson.
Just as everyone inside the stadium was nodding off at half-time, Hakim Ziyech drew a routine save from the goalkeeper before Antonio Rudiger blasted harmlessly over.
That only served to spark City into life though. Gabriel Jesus brushed off Andreas Chistiansen and squared for Sergio Aguero, and while the Argentine's touch was poor the onrushing Sterling steamed onto the loose ball and stabbed it into the net. Cue jubilant scenes on the bench, with the backroom staff gleefully praising Jesus and Kyle Walker leading the celebrations from the bench bouncing up and down waving a scarf in the air.
City sensed the chance to kill the league once and for all as Chelsea hurried to bring on a substitute for the injured Christiansen, and before they could bring on a replacement they had conceded a penalty as Billy Gilmour clipped the heels of Jesus.
Up stepped club record scorer and the most adored man in the squad, Sergio Aguero, ready to make safe his fifth Premier League title from the spot and remind potential suitors of his finishing. The run-up was nonchalant, Edouard Mendy fell to the floor and saw the ball drifting straight down the middle of the goal. And drifting. And drifting. So slow was the panenka that the goalkeeper had time to get to his feet and catch it, blood threatening to burst out of Guardiola's body as he saw a golden chance to wrap up the title float feebly away.
It was so bad it was reassuring in a way, a small glimmer of Typical City from a team that are so ruthlessly brilliant in 98 per cent of their play. This side has become the first since Spurs nearly 20 years ago to miss four consecutive penalties in the league, and even more remarkably they have been missed by four different players.
You suspect from Guardiola's reaction that Aguero will not be called upon to take a spot kick in the Champions League final, yet the Argentine was given the chance to atone in the second half rather than being butchered in the dressing room.
City only needed to muster a fraction of the passion showed by the fans outside the ground who had welcomed them into the stadium but the spark on the pitch had gone, the team instead getting flatter and flatter to give Chelsea encouragement to get back into the game. Nathan Ake did a fine job of keeping Reece James quiet but there were only so many times the visitors could be given space on the edge of the penalty area before they made it count and Ziyech's low effort beat Ederson just after the hour mark.
Even an equaliser couldn't raise the performance levels. On came Phil Foden and Ilkay Gundogan but it was now Chelsea who felt the momentum was with them to seal an away win that would be incredibly valuable in their push to secure Champions League football for next season. The offside flag denied Callum Hudson-Odoi when he thought he had swept in a winner in the final 10 minutes.
Guardiola and the bench were left furious by the decision not to give a penalty when Sterling went down, and the manager had only just finished complaining when Marcos Alonso scored a winner for Chelsea
Ultimately it was a disappointing afternoon given they had the title in their hands and let it pass them by. It would take a slip bigger than Steve Gerrard proportions for them not to win the league, and any dropped points from United in their three matches before the Blues travel to Newcastle will be enough to crown them.
Should United win all three and reduce the gap to five points, it will produce some jitters that may be reactionary but shouldn't have been needed in the first place.
City will be crowned the best team in England, and have seen that they have nothing to fear in the Champions League final. Their success would have been all the sweeter though had their record scorer done what has made him so loved at the club.
Aguero's wait for a fairytale ending goes on.