Although there have been some great moments in Detroit Lions history, they have been few and far between. The Lions haven't won a championship since the 1950s, and since Barry Sanders retired they haven't even been competitive. They are most known for their losing in the 2000s and becoming the first team to ever go 0-16.
While things are finally starting to look up, it has been a difficult journey to get to this point, and even now there are no guarantees that the Lions will finally turn things around. This is why the Lions are considered the most difficult NFL team to root for.
The Business Journals' On Numbers did a study to figure out which teams are the hardest for fans to root for. The study is based on a formula where half of the fan difficulty score is based on ten-season record and the other half is based on landmarks, which includes things like the most recent championship, appearance in a championship game and historical things like that. Based on this formula, the Lions scored a 9.6717 in the fan difficulty index, which is the highest in all of the NFL. The next highest fan difficulty index is 7.216 and belongs to the Browns.
Obviously you didn't need a study to tell you how hard it has been to be a Lions fan, but hopefully dealing with all of the losing is about to pay off and this fan difficulty index will go down in a big way in the coming years.