Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: Ryan Bertrand believes Chelsea made a mistake in letting him go, but it is a desire to improve rather than prove anyone wrong that is driving on the Southampton and England left-back. Eyebrows were raised last year when the much-vaunted 25-year-old departed Jose Mourinho's team for St Mary's, where a summer talent drain left onlookers predicting a season of strife. However, Southampton have proved the 'perfect match' and provided Bertrand with everything he hoped for - stability on and off the field, plus the stage to play regularly for an ever-improving side. The initial loan move was made permanent in February when Saints forked out £10million, ending his long association with Premier League champions Chelsea.Chelsea academy graduate Ryan Bertrand believes the club made a mistake in letting him go, but insists he is happy at SouthamptonAfter impressing initially on loan, Bertrand signed for Southampton permanently for £10m in February this yearBertrand has continued his fine form and has earned an England recall 
 Question:'For me it wasn't a case of 'my career didn't go right, I'm not playing for _',' Bertrand said.

Chelsea