The reality of the avatar state

someone is stressed out, as he has a big presentation that would take his company from being small, to becoming real big in the "whatever" industry

a meditation guy will tell him to relax, but he can't as "all his thoughts are centered in the presentation" thus he continues being stressed out, so the guru would tell him to "think of nothing", taking out everything from his mind, mainly the presentation, when he achieves that, he is able to relax

now substitute "presentation" with "worry about Katara, being in love with her AND if she might feel the same way", and "think of nothing" with "forgetting his earthly attachments"; and last but not least, "relax" with "going avatar state"

the Guru said to avatar

"It deals with pure cosmic energy and is blocked by earthly attachment. Meditate on what attaches you to this world."

than aang thinks of he and katara getting closer, almost kissing

than Guru says

"Now, let all of those attachments go. Let them flow down the river. Forgotten."

Aang: (startled) What? Why would I let go of Katara? I...I..I love her.

Guru Pathik: (reasonably) Learn to let her go, or you cannot let the pure cosmic energy flow in from the universe.

than this is what becomes interesting

Aang: I'm sorry, but I can't let go of Katara.

Guru Pathik: (calmly) Aang, to master the Avatar State, you must open all the chakras. Surrender yourself.

Aang: (reluctantly) Okay, I'll try.

(Aang focuses his concentration. Inside his mind, we see mountains beneath a starry sky. The heavens begin to spin with great speed, the stars blurring streaks that disappear behind the mountains. An image of Katara appears, and drifts back toward the horizon to finally vanish with a twinkle of light. The heavens cease to whirl.)

Guru Pathik: (voice-over) Now, think of your attachments and let them go.

(An image of Katara appears, and drifts back toward the horizon to finally vanish with a twinkle of light. The sky ceases to spin.)

Guru Pathik: (voice-over) Let the pure cosmic energy flow.

Looking up into the stars, we see an aurora of light. Aang is seen floating in space above the planet, and the aurora solidifies into a radiant bridge beneath his feet. Turning from the world below, Aang sees a massive entity standing above snaking path. It is a spectral figure of Aang himself, the tattoos and eyes shining with the light of the avatar state. Aang sets off carefully towards it, mouth open in awe. As he nears the feet of the hovering apparition, his own tattoos begin to shine with light. The towering, spectral Aang descends, a sphere of light shimmering between its fingers. The Avatar is enclosed within this shell, but suddenly he is distracted by a cry of distress. Aang sees a vision of Katara chained to a wall, demanding to be freed. He leaps from the hands of the apparition, and the sphere of light vanishes. Behind him, the great entity fades from sight, as he rushes back down the path. It too begins to fade rapidly, until it drops him to plunge screaming toward the world. Aang suddenly starts from his meditative trance.

Aang: (rising in alarm) Katara is in danger! I have to go.

(Aang turns and races away, sliding down the roof the tower)

Guru Pathik: (calling after him) No Aang! By choosing attachment, you have locked the chakra! (Aang draws to a stop) If you leave now you won't be able to go into the Avatar State at all!
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notice that he did choose to go to Katara, and that on the next episode he was able to almost reach the 7th chakra again even when katara was physically present, so it was not locked at that moment despite what the Guru said, what locked it was his near death thanks to Azula which I will show later

the mistake a lot of us make is to think that letting go is something permanent, actually is a momentary thing WHEN THE AVATAR wants to go avatar state, forget the earthly attachments while reaching for the cosmic energies, after his duties are done, than he can go back to his normal life.

in COD

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Aang wearily picks himself up and looks around. Many Dai Li agents jump down from the cliffs above, forming long rows behind Azula and Zuko. Katara gains consciousness just as the Dai Li surround her. Katara bends the water from the channel and forms a ring of water around her. The water sprouts eight tentacles as she enters the octopus stance. Aang enters his fighting stance and prepares to face his many opponents. He then looks to Katara, who is desperately fighting off the Dai Li agents.)

Aang: There's too many.

(Aang remembers what Guru Pathik told him at the Eastern Air Temple.)

Guru Pathik: (in Aang's memory) The only way, is to let her go.
Aang: (sadly) I'm sorry Katara.

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notice that he left Katara BY HERSELF, NOT "I don't love you anymore"

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Aang turns around and earthbends several crystals out of the ground to form a tent over him. Aang sits down and begins meditating. We enter inside of Aang's mind, where he once again comes face to face with the avatar spirit residing inside him, high above the world and surrounded by the starry heavens. The avatar spirit surrounds Aang in a swirling orb between its hands, and Aang's arrow glows. Shift back to the physical world. Aang's arrow begins to glow here as well, illuminating the crystals that surround him. Zuko and the Dai Li are frightened but also enchanted by this light. Finally, Aang opens his eyes, which glow with great intensity. An incredible explosion of spiritual power destroys the crystals. The Dai Li agents shield themselves from the blast. Aang rises from the ground in a bright pillar of cosmic light. Katara looks up at Aang, hope returning to her. Aang levitates in the air, until suddenly, a bolt of lightning strikes his body. Cut to an extreme close up of Azula's eye where the image of Aang writhing in pain is reflected.

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we can see that he focused in the task at hand, and let Katara defend herself, and ALMOST reached the 7th chakra UNTIL Azula attacked him

so basically

He let go his earthly attachments while deciding to go to meditate in order to reach avatar state

but he didn't give up Katara becoming his wife in the future (if she returned his feelings)

very well said, thats wait ive been trying to say all along, he let go of katara as what attaches him to this world but not as his true love/future wfe. so what all the zutarans are saying is false, aang can still have the love of his life AND still be able to control the avatar state when necessary