Oh.
Korra was going to kill herself.
That’s what the slow motion shot of the tear falling off the cliff meant.
If she’s the avatar and she can’t bend she might as well die so there can be a new avatar.
Or else the world would be without an Avatar and there’d be another hundred year war.
So by deciding that suicide was a good idea she had given up all worldly attachments (including Mako) which was what Aang had to do unlock the Avatar State as well in season 3.
This is exactly how I saw it. It wasn’t that Korra thought she was completely useless as a person without her bending, but that the entire world would suffer without a fully realized Avatar, meaning one that is a master and controller of all bending elements, not just one.
Korra’s entire life had been about being the Avatar and being there to protect the world and those she loved, and that had all been taken away from her. As the other Air Nomad Avatar had told Aang, and Avatar’s duty is to the world. Perhaps it is part of an Avatar to change their self worth and base it upon how fit they are to serve the world, which is probably how Korra was viewing the situation. Whatever it is, Korra showed immense strength, albeit in a very sad way, at even considering giving up everything to give others a chance for peace. She believed that the only way to keep peace and balance in the world - and therefore, the only way to protect those she cared about - was to pave the way for a new, fully realized Avatar. And she was willing to give up everything for the sake of the world.
And despite what many others have said, I believe Korra got her bending back on her own by giving up earthly attachments and doing what she thought she could never do - reaching the spirit world and calling upon the legacies of those that were inside of her to help. If Korra had been a weaker person, none of that would have happened. Korra stood proud and strong at the end of the finale through her own strength, which also consisted of accepting that sometimes she may need to accept the strength of others to get to where she needs to be.
(Source: the-humans-from-wall-e)
