app/views/shared/_errors.html.erb
<% if object.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(object.errors.count, "error") %> prohibited this apology from being saved:</h2>
<ul>
<% object.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
</ul>
</div>
<% end %>