Here are some factors to consider:
* The Avatar: The Avatar is the only one who can naturally master all four elements. This is due to their connection to the spirit world and their past lives.
* Bloodlines: Traditionally, bending is passed down through bloodlines. This means you're more likely to inherit a bending skill if your parents or ancestors possessed it.
* Training: While bloodlines are a factor, rigorous training is essential to develop bending skills. A strong will and dedication are key.
* Spirituality: Bending is deeply connected to the spiritual world. Many characters show a connection to their element through spiritual practices and understanding.
* Special Circumstances: Throughout the Avatar universe, there are instances where individuals learn bending outside of the traditional means:
* Non-Benders learning bending: Katara and Sokka learned waterbending from Master Pakku, who initially believed only Southern Water Tribe members could learn it.
* Bloodbending: This rare and dangerous bending art was seemingly taught only to a few individuals, like Yakone, who then passed it down to his children.
* Metalbending: Toph Beifong, a blind earthbender, discovered metalbending through her heightened senses and connection to the earth.
Conclusion:
While the Avatar has the unique ability to master all elements, the possibility of learning multiple bending styles exists for others depending on their connection to the elements, training, and even some degree of chance. It's not a guaranteed ability, but a potential one.
The Avatar universe offers many examples of characters who defy traditional boundaries and demonstrate that the potential for bending is not limited by bloodlines or conventional wisdom.