title: Why I can't directly set console.log() as callback function
body: <p>Why this code doesn't work    </p>
  
  <pre><code>function callback(num, func) {
      for(var i = 0; i &lt; num; i++) {
          func();
      }
  }
  
  callback(4, console.log("Hello"));
  </code></pre>
  
  <p>I know I have to do like this:</p>
  
  <pre><code>callback(4, function() { console.log("hello"); });
  </code></pre>
  
  <p>But I still don't understand the reason why I have to do like that.</p>