Random attacks by Indian tribes. The frontier had swamps-to-mountainness terrain. Seeds didn't work in all parts of America, some lived healthy in one area while the same seed could die somewhere else there.
The people in Africa, sub-Saharan Africa more specifically, did not had their own written languages throughout their history. This meant that they were not able to preserve their cultural heritage in a written way, and that of course can be a problem on the long term. In order to preserve their culture, the African people used the oral way of keeping the traditions alive, mostly by telling stories to the younger ones, thus it was continuing from one generation to other. Also, the music and the dances where crucial for the preservation of their culture, by being able to see and hear the sounds and dances of their ancestors, they were able to easily accept and be interested in their culture, thus learn it, and continue to keep it alive.
Medicine. Most of the things we consider medicine are only helpful if we're already in bad condition, taking medicine while being completely fine can have terrible side effects on your body.
Democracy, it keeps away a tyrannical overlord from controlling the control, but sometimes it's impossible for different sections of government to agree on certain things, and this prolongs the process sometimes making democracy seem a little unreliable compared to the fast paced solidified decision of a single ruler.
Eating. Doing anything in excess can be harmful, but especially eating in the case of most Americans. Even with the health reforms of today, and dietary programs, many Americans are obese and suffer from type 2 diabetes simply from over-eating.
Those are just three examples I could think of.
