ていくMovement away or development from now onward
ていく presents an action as moving away from a reference point, or a change or activity as continuing forward from that point in time.
Action or movement away from here
With physical actions, the construction can show someone doing something and then leaving, carrying something away, or moving farther from the current location.
明日の会議で使う資料を、佐藤さんが先に会場へ持っていきました。
Ms. Sato took the materials for tomorrow's meeting to the venue ahead of us.
AnalyzeThe materials move away from the current place toward the venue.
猫は魚をくわえていった。
The cat carried the fish off in its mouth.
AnalyzeThe cat takes the fish and departs from the narrator's location.
鳥が海のほうへ飛んでいった。
The bird flew away toward the sea.
AnalyzeThe bird's movement proceeds away from the observer.
Change or continuation from now onward
With a trend, change, or continuing activity, physical travel is no longer required. The construction looks forward from the reference time and presents the process as extending beyond it.
これからも、この森を守っていきます。
We will continue protecting this forest.
AnalyzeThe activity continues forward from now.
町の人口は今後も減っていくだろう。
The town's population will probably continue to decline.
AnalyzeThe decline is viewed as a trend extending into the future.
その日から、二人は少しずつ信頼を深めていった。
From that day on, the two gradually deepened their trust.
AnalyzeAlthough the sentence is past, the process moves forward from the explicitly named past reference point.
Forward from the reference point versus up to it
ていく looks away or forward from the reference point. By contrast, てくる looks toward that point, or follows a development from the past up to the present.
More examples
帰りに飲み物を買っていきます。
I'll buy a drink to take along on my way back.
AnalyzeThe purchase is followed by movement away toward the speaker's destination.
子どもたちは手を振りながら歩いていった。
The children walked away, waving their hands.
AnalyzeTheir movement proceeds away from the observer.
オンラインで働く人はこれからも増えていくでしょう。
The number of people working online will probably continue to increase.
AnalyzeThe increase is projected forward from now.
この経験を今後の仕事に生かしていきたいです。
I want to keep applying this experience to my work in the future.
AnalyzeThe intended activity extends into the speaker's future work.
夕方になるにつれて、風は少しずつ弱まっていった。
As evening approached, the wind gradually weakened.
AnalyzeThe weakening develops forward through the past period leading into evening.
この町はこれからもっと便利になっていくと思います。
I think this town will become more convenient from now on.
AnalyzeThe town's change is viewed as continuing beyond the present.