What is the most difficult concept to learn in statistics and why? Submission I

What is the most difficult concept to learn in statistics and why?
Submission Instructions:
– Your initial post should be at least 200 words/numbers or a combination of both.
– Must be cited, and formatted in the current APA style.
** This is basic Statistics. Subjects include:
– Introductions to Statistics
– Descriiptive Statiscs
– Probability
– Discrete Probability Distributions & Normal Probability
Distributions
– Hypothesis Testing, Confidence Intervals, Correlation, &
Regression