What does "being on edge" mean in this paragraph? I have a book about how to be cool person. the book has a paragraph: "Second, you have to react slowly instead of always being on edge. Do not be the type of person who jumps ten feet if something unexpected occurs, like when someone accidently shatters a glass or a balloon pops. You should also take care not to drop whatever you are doing immediately every time someone shouts your name, or worse, when someone yells, “Hey stupid!” Can you explain the meaning of "being on edge" in this paragraph? Thank!