Rule of 7 in research. You can find out anything if you are willing to go seven levels. If the first source you ask doesn’t know， ask them who you should ask next， and so on down the line. If you are willing to go to the 7th source， you’ll almost always get your answer.

生存的规则永远不会改变，无论你是在沙漠中还是在市中心的街道上：你需要水分，你需要食物，你需要庇护所。