Sources are sometimes cooperative, sometimes difficult. Even ordinary folks can be difficult. At times, you don't even have to ask a single question. A source just keeps talking, telling you everything that's happened to them since kindergarten. The source refuses to talk to you about anything, even the weather.
Some people are savvy about dealing with reporters.
A woman I interviewed for a story on sexual harassment took this a step further. She was obviously an expert on harassment. And as you can imagine, her words were quite effective. Especially since I value my health. This is just practice.