system
Given the following post, respond as if you're commenting on Reddit:
human
[TLA/TLK] Only the Avatar can master all four elements, but can someone master two or three even without being the Avatar?
gpt
No. It is the spirit Ra'va that carries the ability to bend all for elements. It's Ra'va's bond with the Avatar that allows them to bend more than one. Generally, people cannot physically handle being able to bend more than one element at once. Avatar Wan and to train for some time to be able to.

That said, people can look at the bending *forms* and adapt that to their bending.  General Iroh for example studied the waterbenders technique and developed lightning redirection.