It has been a summer of acknowledging costly mistakes.
Manchester United spent £89.3 million on re-signing Paul Pogba, who left Old Trafford for Juventus for just £800,000 in 2012.
Real Madrid exercised their £26m buy-back clause on Juve's Alvaro Morata, who was considered surplus to requirements in 2014 and left to join the Old Lady in a £17m deal. Chelsea are making huge efforts to sign Romelu Lukaku from Everton, after the Belgian was sold by Jose Mourinho for £28m in 2014.
And yet at the same time, Atletico Madrid have gone in the opposite direction by selling local boy Borja Baston to Swansea.