app/views/shared/_error_messages.html.erb
<% if object.errors.any? %>
<div id='error_explanation'>
<h2><%= t('errors.count', count: object.errors.count) %> <%= t('errors.message') %>:</h2>
<ul>
<% object.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
</ul>
</div>
<% end %>