To learn from what you want to know, I explained that it is necessary to grasp the overall picture roughly.

Some people seize this words "grasp the overall picture" heavily. They misunderstand that they can grasp the overall picture after studying hard. In the phrase "roughly grasp the overall picture," the most important word is "roughly." The next important word is "overall." Rather than seeing only a narrow part in detail, see the whole part roughly. 

By doing that, when you need to find something, you can narrow down the search range, saying "I think it was around here."