Surprises come in all forms. They can be positive or negative. AC Milan had their fair share of both this season.
The unexpected form of Juraj Kucka and M'Baye Niang were certainly positives. Gianluigi Donnarumma probably qualified as more of a shock.
But the biggest surprise of the season for the Rossoneri wasn't so pleasant.
Milan made three big-money signings this past summer. Striker Carlos Bacca and center back Andrea Romagnoli, who cost €30 million and €25 million, respectively, both had successful seasons. Bacca finished third on Serie A's scoring chart, and Romagnoli made great strides in his development towards being Milan's next top center back.
But the other big signing—one that set Milan back another €20 million—hasn't panned out as well, and the degree to which it has failed is probably the biggest surprise of Milan's season.
Andrea Bertolacci was a second choice. After a deal for top midfield target Geoffrey Kondogbia fell through, Milan vice president Adriano Galliani was left scrambling to find an alternative.
Bertolacci had attracted attention over the previous seasons at Genoa. Last year he finally had a true breakout, scoring six goals and recording eight assists. WhoScored.com clocked him at 1.4 key passes, 2.1 tackles and 1.3 interceptions per match.
After the Kondogbia deal fell through, Galliani focused in on Bertolacci as his secondary target. He splashed €20 million to get him from Roma, who had co-owned him with Genoa for several years.
Bertolacci was expected to play a big role in Milan's midfield this year. Expected to be a box-to-box presence who could help create and contribute defensively, he was considered one of the keys to the team's success.
But it didn't turn out that way. Bertolacci's play was one of the biggest disappointments in Serie A this season.
To be fair, a lot of the criticism the 25-year-old has received has been overblown, mainly because of his transfer fee. When a team pays €20 million for someone, they expect big things.
The problem is that Bertolacci has never really been a €20 million player. Setting his breakout year aside, he'd never scored more than four times in a season or notched any more than three assists.
The majority of the transfer fee derived from the fact that he was young and Italian. For Galliani to spend so much was a significant overpay.
Bertolacci wasn't likely to justify such a fee, but his season this year was horrible by any standard. He only scored once and notched one assist.
His playmaking completely fell off. While his pass completion percentage ticked up by more than two points, he averaged only 0.8 key passes per game. He wasn't putting the ball on goal either, only averaging 0.7 shots after 1.8 and 1.6, respectively, over the previous two seasons.
He eventually saw himself drop out of the automatic starting XI. What was supposed to be a major asset ended up being a huge liability. Considering how weak Milan's midfield turned out to be this year, Bertolacci's vanishing act was particularly harmful to their efforts.
While he was never going to justify his overblown transfer fee, Bertolacci is still a better player than what he showed in the 2015-16 season. His complete lack of contribution over the course of the last year has been nothing short of shocking.
There is still time for Bertolacci to turn his move to the San Siro into a success. His contract runs for three more years, and Milan are unlikely to give up on him easily given the investment they made in him.
Whether he manages it is a question for the future. But in the present, he is definitely the most disappointing—and surprising—player on Milan's roster this year.