An amended pleading is a change to an original filed pleading that is made before any response is given. A person that files a pleading only has the time before the response is filed to make any changes. Otherwise, the pleading will stand as originally filed even if it is missing a material fact. A case can be thrown out if a vital piece of evidence is not listed in the original pleading and not refiled in time. This would cause a loss of opportunity to progress the case without starting again.
A pleading can only be amended with a material fact that was not referred to in another way. It cannot be made redundant through non-exhaustive explanations. If new evidence comes to light or is materialized after the filing of the original pleading, it plays an important factor in a case and can sway the judgment.