Perhaps our failure is [the] [failure] to distinguish . . . . . .

I wrote this as "Perhaps our failure is to distinguish between X and Y."

Then I decided it was incorrect and added the second "failure."

Now I'm not sure it's needed.

Any advice?

Best wishes. - A.

One quick comment is that the way you originally wrote it could be taken to mean this.

We distingushed between X and Y. Perhaps that is our failure.

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Great point, Clive. Thanks.
Just a passing thought....
Perhaps, our failure was the lack of ability to distinguish the difference between X and Y.
Or 'inability'.
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Thanks, guys. [Y]

- A.