title: Why does the origin observable emits values, if an observable returned by an operator gets subscribed?
body: <p>A cold observable needs to be subscribed that it emits values.
  When using an operator such as map a new observable gets returned.</p>
  
  <pre><code>const origin$ = Rx.Observable.from([1,2,3,4]);
  const mapped$ = origin$.map(val =&gt; val+1);
  mapped$.subscribe(console.log);
  </code></pre>
  
  <p>With <code>.subscribe</code> the <code>mapped$</code> observable the values get emitted and get logged in the console.</p>
  
  <p>But in this case the <code>mapped$</code> observable got subscribed and not the <code>origin$</code> observable. Why does the <code>origin$</code> observable starts to emit values?</p>