It is difficult because all people are different. They have different backgrounds and motives and even one person can change over time.
People.
if you eat horse manure it is scientifically proven that they will begin to show signs of developing into a grapefruit
It gives a direction to test in.
blurry vision which makes it more difficult for them to play.
The desert and the governmental repression.
Because of the miscellaneous-nees of the universe, it is a very hard miscellaneous task to study the universe. You have to see the positives in it, you cant be negative about it or the universe will get mad.
silence
Eating chocolate (and eating in general) releases Dopamine in the brain which improves mood. Yes, this release of neurotransmitters is scientifically proven.
If you're talking about what I think you're talking about, the fact that it is not "scientifically valid" might have a lot to do with it.
Fog makes it difficult for people to see. It is potentially dangerous. When people walk out in the road, a car may not see them and run into them.
Read. Reading is a very difficult thing for people with Dyslexia.
Mutilation Makes Identification Difficult was created in 1995.