What are the three most important concepts we discussed in class?

This is the end of the first week of the class. I am curious to know how things look from your perspective, so please respond to the following questions. Answers should be short (no more than 5-6 sentences).
Note: the content of your answers will not be graded, only if you submitted a response.
Question 1: What are the three most important concepts we discussed in class?
Question 2: Which concept did you find the most difficult and why? (could be more than one)
Question 3: Find an article in the popular media that discusses using data for solving problems or supporting decision making. Explain briefly what is the problem and how data is used (here’s an example of an article: http://www.nytimes.com/2016/04/03/sports/baseball/putting-data-science-on-a-players-sleeve.html)