It's possible that the Trait is being used indirectly through another class that already uses it. Check if any of the parent classes or traits of MyController use TraitName.
If that's not the case, it's possible that the Trait is being autoloaded by Composer. Check your composer.json file and make sure the namespace for the Trait is included in the "autoload" section.
If neither of those solutions work, it's possible that there's a caching issue. Try clearing your Laravel cache by running the following command:
php artisan cache:clear