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In the below sentences, the position of 'therefore' seems a bit awkward.

I don't quite figure out why 'therefore' is indispensible in that position.

Rather, it seems redundant.

Do you agree with me?

Thanks in advance.

The Americans are cordial, frank, anxious to oblige, and ready to make friends. In the fullness of their heart, Americans generally promise more than they can keep. Easily excited, they are not seldom deceived by their impressions, which, therefore, are often only temporary.
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You will change the meaning by removing 'therefore'. The word is there to correlate the fact that their impressions are often temporary and the reason why that is so.
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Hi guys,

. . . they are not seldom deceived by their impressions, which, therefore, are often only temporary.

With or without 'therefore', what does this sentence mean?

Clive
Thanks, Ivanhr.