What are specific reasons my Catalytic converter failed on my Chevy tahoe 2005 on 2005 Chevrolet Tahoe

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My tahoe's check engine light came on and there was a rattle in the vehicle when it idled and when I started driving. I took to small shop in Madisonville and was told it was the Catalytic Converter. But your website said it was important to have shop identify why the catalytic converter failed because failure was almost always due to another problem, which if not resolved will quickly ruin a new catalytic converter.
(1) Answer
Best to have a competent shop scan 'live data' and possibly determine the cause from that. If check engine light has been on for a while , the converter may need to be replaced first in order to get readings that are not caused by the failed converter (if it's causing a restriction in the exhaust for instance).Have any maintenance records?.......Got milk?