Cause and Effect
An event i.e. the same event, can be the cause of something, as well as the effect of something else. But that doesn’t mean that cause and effect are equivalent elements, in themselves.
It is not possible to say that X is a cause of anything, till the effect is seen/known or atleast it (the effect) having had crossed the mind (via imagination).
Another way of putting the above is – if you know something to be a cause, you know its effect also. But not vice-versa.
Hence, in a way of speaking, Cause “requires” Effect along with it; Effect “doesn’t require” Cause along with it.
The very utterance of the word ’cause’ implies that the effect is known/imagined before, to/by the mind.