title: Why "() => this.tick()" and "this.tick()" are not the same?
body: <p>I am looking at this code: <a href="https://reactjs.org/docs/state-and-lifecycle.html" rel="nofollow noreferrer">https://reactjs.org/docs/state-and-lifecycle.html</a></p>
  
  <p>I do not understand why I need to use <code>() =&gt; this.tick()</code> instead of just <code>this.tick()</code>. The prior calls a function that uses <code>this.tick()</code>, yet when I change <code>() =&gt; this.tick()</code> to <code>this.tick()</code>, the code stops working. <code>this.tick()</code> is no longer being called even though it itself is a function. <code>() =&gt; this.tick()</code> seems to be just an unnecessary step and yet it is necessary.</p>
  
  <p>I think I am misunderstanding functions as objects. </p>
  
  <p>Thank you</p>