As a further extension of this example, assume Tweedy conceived of the same mousetrap on December 31, 1990. Tweedy never told anyone about the mousetrap and did not work on reducing the mousetrap to practice for many years due to financial reasons. Tweedy finally reduces the mousetrap to practice on February 15, 2006. Tweedy did not diligently work to reduce the invention to practice, so he is not entitled to a patent over Tom or Jerry.<ref>http://www.uspto.gov/web/offices/pac/mpep/documents/0700_715_07_a.htm#sect715.07a</ref> This is one of many reasons why patent attorneys advise clients to file patent applications as soon as possible.
== Comparison ==
The debate as to which system is better is long-running and unlikely to reach a single conclusion. There are arguments for and against both systems.
The first to file system leads to procedural certainty as the filing date of an application can very rarely be challenged. In contrast, the first to invent system leads to uncertainty as the right to grant of a patent can be challenged by a second party and can only be finally determined by extensive consideration of the making of the invention.
It is said{{Who}}, however, that the first to file system favours large companies who can afford to rapidly file patent applications, thereby gaining an advantage over smaller companies who are slower to file due to cost restraints. The first to invent system is therefore said to be beneficial in encouraging the growth of smaller companies. A potential problem with this argument is that a smaller company, filing second, would have to rely on interference proceedings to claim their patent, which may be beyond their economic reach and they are therefore no better off.
