What an Idiot!/Anime and Manga/Death Note

For a show that is supposed to be about geniuses, there are a number of noticeable idiot moments in Death Note.


 * In the second episode of Death Note, Interpol makes a broadcast wherein "L", the greatest detective ever, announces that he will be taking the Kira cases. More importantly, he does this while giving his real name and showing his face for what is supposed to be the first time ever, and is practically daring Kira to kill him right then and there. There is something suspiciously fishy about this.
 * You'd expect: Light realize this was likely to be a trap or probe of sorts and avoid killing the man. Or, if the temptation is too strong, do some research on the name and face to check if its falsified first and then kill him at a later date.
 * Instead: He writes his name in the Death Note right then and there and, big surprise, it was a trap. Now, not only did L figure out his MO and limitations, but he pinpointed his location.
 * After his first failed attempt to kill Near in Death Note, Light Yagami sends the Death Note to Teru Mikami, a definite Kira supporter, with instructions on it.
 * You'd expect: Light to send a message to Mikami to hide a page of the Death Note on his person, considering he must have had Kiyomi Takada do the same herself, and does so himself (using a trick watch to hide it). This would help him handle emergencies, the number of which had lately been high enough for Light to be tempted to kill Sayu with the watch trick. Additionally, for himself, he would make some extra precautions to ensure that he's not on the brink of defeat again.
 * Instead: He does not. This is clear from the fact that Mikami has to go to the bank a second time in a single day in the first place to kill Takada. Light, blinded by his ego and not even instructing Mikami earlier to only enter the warehouse (which has a single exit to begin with) upon hearing a password from him (like what he did in his Memory Gambit), declares his victory in the warehouse too early.
 * Light, still being a student, has been keeping his Death Note activities in the afternoon to late evening. L comments upon this, suggesting Kira is a student.
 * You'd Expect: Light would try and dissuade the notion by suggesting that it is just a coincidence and many people may only be able to attack in the afternoon, not just students, being the Chessmaster he is.
 * Instead: He begins writing down names to die in a more spread out fashion that day the night before, leading L to deduce that the Kira has insider information about the investigation and prompting him to lock everyone in the same room together, which forces Light to actually get on the team to keep up with his opponent.
 * It's the endgame! Light and Near face off in the ultimate battle of wits. The fate of the world rides on these moments. Light's plan? To perfectly recreate the act of using the Death Note with a fake, then ensuring Near swaps the fake for another fake. Essentially, they will have believed that they disarmed him, unaware that they've only captured a harmless copy! Meanwhile, he keeps the real Death Note hidden away, then replacing the fake with the real one at the last moment! That way, the copy they "know" is fake is anything but! That way, when they allow him to incriminate himself, he'll instead slaughter them all at once, and the world will be his!
 * You'd expect that Light The Chessmaster would keep an eye on the real Death Note at all times, test it prior to the epic finish, keep several backups stored, maybe lend that page he keeps in his watch to the assassin, and hey, maybe even a grenade or two just in case. As long as they die, however they die, he wins. And even if they don't, they won't have any evidence directly linking him to Kira.
 * Instead he puts the original in a safe miles away, under no observation, doesn't bother testing it, and then loudly incriminates himself in front of all of them. Then he tries to use a Death Note (ironically, a functioning Death Note page that could have killed them all had he given it to his lackey instead), in front of several people with much faster guns. Twice.