Why do managers struggle after stepping up to 'big-six' clubs?

Why do managers struggle after stepping up to 'big-six' clubs?Image source, Getty ImagesImage caption, Andoni Iraola (left) is set to make the step up from Bournemouth to Liverpool, while Thomas Frank joined Tottenham from BrentfordByPrudent NsengiyumvaBBC Sport journalistPublished1 minute agoMoving from a successful Premier League side to a so-called 'big-six' club is sometimes seen as the natural next step for a manager. By the 'big six' we are referring to Arsenal, Chelsea, Liverpool, Manchester City, Manchester United and Tottenham. We do not use that term to disparage the likes of Aston Villa or Newcastle who have qualified for the Champions League in recent seasons, or indeed any other top-flight team.But those six clubs have largely dominated the top of the table over the past 15 years or so. So will Andoni Iraola, who has reached a verbal agreement with Liverpool, be able to make the step up from Bournemouth after finishing, ironically, in sixth place with the Cherries?The data suggests it is one of the toughest transitions in the game - with short tenures, mixed results and no major silverware won by a manager taking that step within the Premier League.In recent seasons, Thomas Frank, Graham Potter and Nuno Espirito Santo all struggled to make the leap.A series of short spellsFor managers who earn a move to one of the Premier League's biggest clubs, the opportunity can arrive quickly. So too can the scrutiny.The most consistent pattern is how short those spells tend to be. Of the managers BBC Sport has analysed, the majority failed to last two full seasons, with several dismissed before completing their first campaign.David Moyes' appointment at Manchester United in 2013 remains one of the clearest examples. Hand-picked from Everton by Sir Alex Ferguson - who urged supporters to "stand by your new manager" in his farewell speech - Moyes arrived with both backing and expectation. He was dismissed just 10 mont...