The "problem" in the UK only seems to arise if you are English, because, with one notable exception, the Scots, Welsh and Irish seem to be more realistic regarding expectations.
However, the English media fans the flames by persistently insisting, for example, that at least as far as football goes, England should have added to that 1966 win several more times.
That all raises false expectations and hope, as history has shown. Cricket and rugby are no different. Unless England win the Ashes or the rugger World Cup, it gets reported as if it's a reason for national mourning when they fail, as most of the time they do.
This is not an attack on England and all things English, it's just an honest observation. There's absolutely nothing wrong with anyone hoping their national team does well, but let's put it in perspective, it's not really the end of the world if they don't.