don't/can't understand

[user_gary]

I don't understand what you mean.
I can't understand what you mean.

Please tell me what the difference between first and second sentence is.

[Mister Micawber]

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Well, they normally have the same intent, Gary. Natives usually use the first, where ESLs (at least, my ESLs) always want to use the second.

The first states the conditionl; the second states the inability.
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