Explanation:
Firstly, let's understand what an orphan block is. An orphan block is a valid block that is not a part of the main blockchain because it was not added to the blockchain due to a fork. A fork occurs when two different miners solve a block at the same time, creating two different versions of the blockchain. The version of the blockchain that gets the most computational work is considered the main blockchain, and the other version is discarded. The block that was discarded is an orphan block.

Now coming to the answer, an orphan block is not necessarily created only when a 51% attack is successful. An orphan block can be created in any situation where a fork occurs, which can happen due to various reasons such as network latency, software bugs, or even random chance. A 51% attack is a situation where an attacker controls more than 50% of the mining power, which allows them to create a longer chain and overwrite the main blockchain. However, even in a 51% attack, the attacker may not always create orphan blocks.

In conclusion, an orphan block can be created in any situation where a fork occurs, and it is not necessarily related to a 51% attack.