到
dào
到 is not arrival. It is the instant your fingertips touch
The picture Reaching out until your fingertips land on the target. There is a line between not touching and touching. 到 asks whether you touched the point you aimed at; 完 asks whether the amount ran out — 看到了 is it landing in your eye, 看完了 is watching it through to the end.
Where the picture shows up in 到
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reaching a place
我八点就到公司了。
wǒ bā diǎn jiù dào gōngsī le
I got to the office by eight.
Under a clock reading eight, a foot landing on the office threshold and crossing that line.
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reaching me
你收到我的邮件了吗？
nǐ shōu dào wǒ de yóujiàn le ma
Did my email reach you?
A sent message dropping onto the top line of the other person's inbox.
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not reaching it
那本书我没买到。
nà běn shū wǒ méi mǎi dào
I couldn't get hold of that book.
A hand reaching along the shelf, finding only the gap where the book should be, and coming back empty.
买了 says you did the buying; 买到了 says you actually walked away with it.
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the eye reaching it
我昨天在地铁上看到他了。
wǒ zuótiān zài dìtiě shang kàn dào tā le
I saw him on the subway yesterday.
A face in the subway crowd catching at the end of your line of sight.
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reaching a point in time
我们昨晚聊到十二点。
wǒmen zuówǎn liáo dào shí'èr diǎn
We talked until midnight last night.
Two voices carrying on until the clock hand touches the twelve.
All of it in one picture
到 is one picture: fingertips reaching out and landing on the target. Feet landing on the office is arriving; a message landing in someone's inbox is it reaching them. A hand that never lands on the book is not getting hold of it; eyes landing on a face is seeing him; a conversation landing on the twelve is talking until midnight. So 到 does not say you performed the action — it says you actually made contact with what you were after.