title: Difference between first! and first method in Rails
body: <p>What is the difference between <code>User.first</code> and <code>User.first!</code> in Ruby on Rails? </p>
  
  <p>I see the example in the Ruby Guide but there is no explanation between why it's different. As far as I know, <code>!</code> is used to represent that the method is changing the variable. </p>
  
  <p>*<code>User</code> represents a table. </p>