It's more about entitlement than injuries for me, the mentality of entitlement.
When they were nowhere near winning the league for years they used to tell themselves that they were cheated every season by referees etc, like they were a small club, despite the overwhelming evidence to the contrary, and despite being overwhelming beneficiaries of decisions favouring the big clubs.
Now they have a winning team, they convince themselves that everyone wants to stop them being in their rightful place (as they see it).
If you were doing a psychological profile of a person with the same mentality, you'd think of it as a persecution complex. In with that, you then have stuff they're justifiably angry about (Hillsborough), and stuff they should be ashamed of but aren't (Heysel, defending Suarez's overt racism).
The sense of entitlement coupled with the persecution complex makes for quite an unpleasant collective mentality in their fanbase, and as others have said, it becomes quite exhausting as their neighbours and rivals, just putting up with their hissyfits and desire for attention.
As difficult as following Everton can be at times, with it's own psychological challenges, I'm eternally grateful that we're a bit more grounded and that we actually reside on Earth.