Explanation for my doubt

[VishnuSureR]

conditions are only re-checked if a user manually changes a field for a record on a form; if the change is made by a UI action, context menu action ,from an import set, via web services , or through the List Editor , it will not be evaluated. 

could you please any one explain this once , i have do this practically  with UI actions ,but evaluating UI policy condition.