The rise is very hard, the fall is quite easy

Promoted teams are prime candidates for relegation within two years. Significant roster overhaul is almost always necessary the first year, and teams struggle with new players. Usually they have difficulty scoring goals and have to survive with a lot of draws, winning battles with other strugglers, and stealing points with the better-funded squads.

It's inevitable that better players and coaches are prime candidates for the transfer market. It doesn't take many bad results, injuries, and loss in Ferguson time to endanger these teams.

Other examples are Leeds United in the late 90's, spent heavily, severely underfunded, and have been relegated forever once they fell out of the top 6. Not as familiar with Nottingham Forest - European poer in the 70s to way down the leagues nowadays. Also Portsmouth going into receivership - think while in the EPL.