I seem to have campaigns that maybe not fail, but fizzle. A lot of the recent campaigns come to a natural place to end them and we continue playing them. So, I create a new arc to last a few levels to try and play on something from a backstory or a piece of the campaign that was overlooked or forgotten about. This might be cool or ok, but after a while one player, mostly my father, get tired of playing the higher levels (10-14) and wants to start a new campaign.
We had one 4e campaign that I created that failed in concept. We had another player at the time that could only meet every other week or three, so I created a campaign where the PCs are part of an adventurer's guild and each player created 3 PCs and each week we would have a closed game lasting just one night. The idea was to play all three PCs on a rotating basis and create varied parties each week. The regular players all kept picking the same PCs and the random player stopped coming after a few months, so we just made a longer campaign with the 'normal' group of PCs.