Some of the Death Note's rules are really funny if you think of them as clarifications for users, necessary fixes to address exploits, or bugs that the Shinigami king isn't going to fix.
If a Death Note owner accidentally misspells a person's name four times, that person will be free from being killed by the Death Note. -> patch to fix exploit where users would attempt to brute force killing someone by writing every possible name in the Death Note
However, if the Death Note owner intentionally misspells the name four times, the owner will die. -> Patch fix to stop exploit where users would try to grant themselves immunity
The person whose name was misspelled four times on purpose will not be free of death by a Death Note. -> Necessary clarification because users thought they could grant someone else immunity
If the same name is written in two or more Death Notes within 0.06 seconds, the entry is regarded as simultaneous; the Death Notes will not take effect and the individual will not die. -> Rare bug related to When the same name is written in two or more Death Notes, the Note which was used first will take effect, regardless of the time of death. Root cause is server requests first check if the same existing request was already made. Simultaneous requests assume the other request is valid and delete themselves. Will Not Fix. Bug is rare and fixing it could result in new exploits related to repeatedly writing a person's name in the Death Note.
When you write multiple names in the Death Note and then write down one cause of death within 40 seconds of writing the first victim's name, the cause will take effect for all the written names. Also, after writing the cause of death, even if the conditions of death are written within six minutes and 40 seconds in the human world, the conditions will apply only to the victims for whom they are possible. Those for whom the conditions are not possible will simply die from the specified cause. -> Code bug caused by undefined and ambiguous input syntax. Will Not Fix.
Once the victim's name, cause of death, and conditions of death have been written down in the Death Note, the death will take place even if that Death Note, or the part of the note used, is destroyed before the stated time of death. -> Clarification to stop users from pointlessly destroying the Death Note
The Death Note will not affect those less than 780 days old. -> A patch added to get around various cultural arguments related to when something is considered "Human"
You cannot kill humans who are more than 124 years of age with the Death Note. -> Added in reference to a Shinigami meme
You cannot kill humans with less than 12 minutes of life left (in human calculations). -> Patch that addresses undefined behavior from edge cases where the victim dies naturally before the Death Note can normally take effect or during the window the user can write additional details to the cause of death.