过
guo
过 is a stamp in your passport
The picture A stamp thumped into a passport. It proves you passed through once; it does not mean you are there now. 过 leaves only the trace of passing; 了 changes the state you are in now. 他去了上海 means he went and is there; 他去过上海 means the trip left a mark and he is back here.
Where the picture shows up in 过
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a place you passed through
我去过上海。
wǒ qù guo Shànghǎi
I have been to Shanghai.
You open the passport and there is the Shanghai stamp, while you yourself are sitting here.
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a stamp from this morning
你吃过早饭了吗？
nǐ chī guo zǎofàn le ma
Have you had breakfast yet?
On this morning's table sit an empty bowl and a spoon washed and turned face down.
过 is not only for once-in-a-lifetime things. A stretch as short as this morning can carry a stamp.
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no stamp at all
这个药我以前没吃过。
zhège yào wǒ yǐqián méi chī guo
I have never taken this medicine before.
You open the bottle and the pills are exactly as many as the day you got them.
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one stamp, counted
我见过他一次。
wǒ jiàn guo tā yí cì
I have met him once.
Beside his name there is exactly one stamp in the box, and no second one.
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a stamp your ears kept
你听过这首歌吗？
nǐ tīng guo zhè shǒu gē ma
Have you heard this song?
The first bar plays and your head is already nodding along before you decide to.
All of it in one picture
The passport stamp is the mark of a place you passed through; the upturned spoon is the mark this morning left behind. Untouched pills mean there is no stamp at all, the single stamp beside his name is a mark someone counted, and the nod at the first bar is a mark your ears kept. All five show you not the present but what stayed behind after the passing. Read 过 as a trace left rather than as having tried something, and it stops slipping.