Failure is relative though isn't it. We've had how many F.A cup semi finals and play off final days out at - ok we've lost them all, but that's still a lot more than some clubs of a similar size have experienced. Many of the similar sized clubs have had more success than us in my time such as Stoke and Derby but at the same time they're not exactly having the time of their lives now, look at Wednesday also for a club that's really struggled for over 20 years.
Leeds who are a big club, don't like saying it but it's true, they've had a terrible 21st century on the whole, we've done better than Leeds too in that time and beaten them to promotion twice! So it may be failure in comparison to many clubs but others would swap our last 20 years for theirs, I'm sure of that.