Customizing Model Validation error messages alerts

You can use :message option to assign custom error message.

Example:

validates :directions_from, presence: true, 
  message: "'Direction from' really really really can't be blank!"

Then this custom error message will appear as <%= msg %> in the form view.

Ref: http://edgeguides.rubyonrails.org/active_record_validations.html#message

Add To answer OP's question on the comment, i.e. the message shown in web page is not very friendly, showing result as "Directions directions from 'Direction from' really really really can't be blank"

The reason is the view template use errors.full_messages to show the error messages. You can easily customize it with two options:

Option 1: Write the custom message without subject. i.e. really can't be blank

Option 2: Write the message as before in full sentence, but refer to message only in view, instead of full_message

Example:

<% @hikingtrail.errors.messages.each do |msg| %>
    <li><%= msg %></li>
<% end %>

Ref: http://rubydoc.info/docs/rails/3.2.8/ActiveModel/Errors (full_message is nothing more but a mix of attribute and message)