No offense meant but I think that's nonsense personally. No team's ever won stuff due to fans' optimism. Nor do they lose out on trophies because the fans have a pessimistic outlook.
It's the other way round actually. teams win stuff because they're good enough which breeds an optimistic attitude amongst the fans. The more sustained the success, eg. the rs under Shankley, Paisley, Fagin and Dalglish or Utd under Ferguson the more accustomed the fans get and the more ingrained that attitude becomes.
This then translates into what we often refer to as a sense of entitlement eg. rs and Utd fans. To a lesser degree, Arsenal fans. A whole generation of whom have watched their team qualify for the Champions League and win trophies on a fairly regular basis.
And, obviously, the opposite is true. The longer a club goes without winning stuff, the more fatalistic the fans become.