get_the_excerpt doesn't work on archives page?

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‘get_the_excerpt’ works fine on all of my pages but the archives page, and I’m thinking it’s because I copied some code from a tutorial that uses $wpdb, which mysql to display information, and that is what’s throwing me off. Mainly because I don’t really understand php, yet alone mysql.

$theid->ID works on most things (like category, titles, and EVEN Thumbnails!) but not for the excerpt.

What is going on?