There are many wishes granted by the characters in Dragon Ball through Shenron, the Eternal Dragon. However, not all wishes can be fulfilled, and there are some that even Shenron has to “throw in the towel” and cannot realize fully.
Below are the wishes that cannot be granted:
1. Sacrificing One Person Twice
This rule has occurred with Goku and his friends when they attempted to sacrifice Krillin during a fight. The Z Fighters wanted to sacrifice Krillin for the second time, but Shenron could not grant that wish because those who have already been wished back cannot be sacrificed again. To clarify, each person can only be wished back once.
However, this limitation only applies to Shenron of Earth, while Shenron on the planet Namek does not have this restriction.
2. Taking a Stronger Life Form’s DNA to Create a Dragon Ball
The idea that Shenron cannot take DNA from a stronger being to create a Dragon Ball is a confirmed rule. For example, it has been stated that Shenron cannot take DNA from a creature stronger than itself. Since the Saiyan Saga, there have been many powerful beings that have appeared who are known to be stronger than Shenron.
3. Granting Multiple Wishes
Shenron cannot grant many wishes for one person. If the user does not accomplish their wish, they may have to wait for thousands of years to have their wish granted again.
Initially, the user could have one wish, but later on, Dende modified it to allow for 2 or 3 wishes, depending on the wish made.
However, this may not be the case regarding the Super Shenron in Dragon Ball Super. As previously mentioned, Super Shenron can grant any wish. Therefore, anyone can freely wish for anything that they desire, even if it is something like: “I want a million wishes.”
4. Sacrificing Those Who Have Already Passed Away Due to Natural Causes
Another wish that Shenron cannot fulfill is sacrificing those who have already passed away due to natural causes (such as old age or illness). For instance, Goku in the future had already died from heart disease, and thus Shenron could not revive him.
Shenron can only bring back those who have died due to some violent action or event.
5. Changing the Time Limit of the Dragon Balls
A fundamental rule regarding the Dragon Balls is that after a wish is made, the Dragon Balls will turn to stone for a year and cannot be used again until then.
This is a core rule of the Dragon Balls, so it cannot be bypassed by using any wishes with Shenron.
