Mistakes.

Now in Dragonball Z...The characters such as Goku makes mistakes...or bad decisions some might say. Here below, are a few mistakes or 'bad decisions' made by the characters.

Goku
Mistake(s): Believe it or not, the great Goku has made his fair share of mistakes in the series. The biggest would be allowing Dr. Gero to live. By doing that, the androids were able to take over, and it was because Goku allowed Dr. Gero to live that the androids and Cell were created. Another big mistake would have to be transporting Cell to king kai's planet which exploded but allowed cell to get even more powerful.

Vegeta
Mistake(s): Where do I begin?? Vegeta has made more mistakes that probably anyone. The big one being allowing Cell to become Perfect so that Vegeta can have a challenge. Another would be allowing Dr. Gero to awaken androids 17 and 18. Then of course there was the whole Frieza thing in which he was killed by Frieza but at the time, he was really the only one had a shot of a chance against Frieza.

Gohan
Mistake(s): Gohan has not made a huge amount of mistakes, but nobody is perfect. During the Cell Games, Gohan was holding in a lot of power and basically toying around with Cell even though he honestly could have killed him from the begginning. By not killing Cell right away, Cell started to grow like a balloon and it forced Goku to transport to King Kai's planet where he died. Another mistake would probably be trying to take on Buu when he first saw him because he just got knocked out badly.

Future Trunks
Mistake(s): Future Trunks has only made at the most a couple noticable mistakes. The biggest being fighting Cell in the USSJ form which was a very slow form.
Mistake(s): Krillens number one mistake would probably be not destroying Android 18 when he had the chance. If he blew her up, then Cell would not have become perfect. Then Vegeta would have easily killed him.

Other mistakes.

The First-Year Aging Problem
The first year of the series. Goku is 12 and Bulma is 16 at the start of the series, and a year after the Dragon Balls are used and they revive, Goku is still 12 and Bulma is still 16 when they are asked.

Any One Wish?
When Goku asks Shen-long if he can revive Bora, he says "There is no wish I cannot grant." We see time and time again in DBZ when Shen-long can't grant a wish asked of him.

Do Nameks eat?
When Mr.Popo recounts Kami's story of how he came to earth, we see Kami in Yunzabitt Heights, where he landed there was no "suitable food." However, when Bulma, Gohan, and Krillin go to Namek, Dende says that Nameks don't eat, but only drink water. Then how would it matter to Kami if there was no food at all in Yunzabitt Height?

Trunks can't count!
When Trunks first appears from the future, he warns Goku about the two Artificial humans that terrorize the future, he says they are #19 and #20. However, when he returns to the future and sees #19 and #20, he has no idea who they are. He then tells Z warriors, the ones that were really terrorizing the future are #17 and #18 and not #19 and #20.

The Nameks aging paradox..
When Piccolo (Jr.) was first born it took 3 years for him to mature to nearly his full growth. But it took Dende 20 years to mature to a fully grown Namekian. One would wonder why there would be such a difference in the time it takes for a Namekians to age!

The Lump in Cell's Head..
After Cell comes back after blowing himself up, he says that there is a lump in his head that allows him to regenerate as long as it is undamaged. This seems contrary to the fact that Goku blew off Cell's head and shoulders with a Kamehameha only an hour or so earlier.

The Dragon Radars
During the Buu saga, Bulma tells Goku that the Dragon Radars are made with special parts that cannot be replaced if destroyed. However, way back during Goku's run-in with Blue in Penguin Village, Turbo made a Dragon Radar out of parts from an ordinary airplane.

But i think...the biggest mistake made...was the mistake...supreme kai made. He said he had the oppotunity to destroy Buu once and for all or something, but he didnt. Because of this...the future people of earth had to suffer. Some Kai he is.

INSTANT TRANSMISSION