Time passes, and we cannot stop it.

However there are some things left after it passes,

such as its trace and our memory.

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Looking back nostalgic memories which are trace of time, 

we can vaguely suppose something actually happened

in the past.

This is sometimes so ambiguous that even the person who has gone through that feels unsure if they really have.

Also in our mind memories can be misplaced and mixed not in the right order.