title: Why Symbols not convert string implicitly
body: <p>Why <code>Symbol('test').toString()</code> works well, but I can't use <code>'' + Symbol('test')</code>?</p>
  
  <p>It will throw Error: </p>
  
  <blockquote>
    <p>cannot convert a Symbol value to a string</p>
  </blockquote>
  
  <p>Why does the implicit type conversion not work? Why is the code not equal to <code>'' + Symbol('test').toString()</code>?</p>