Why doesn't the MYSQL trigger fire?

Question

MySQL

There are the following tables:

users
id, discount, ...
coupons
id, code, ...
discounts
id, user_id, discount, ...

The following restrictions are configured:

ALTER TABLE `discounts`
  ADD CONSTRAINT `discounts_ibfk_1` FOREIGN KEY (`user_id`) REFERENCES `users` (`id`) ON DELETE CASCADE;

When deleting records from the discounts table, the trigger fires:

CREATE TRIGGER `after_delete_discounts` AFTER DELETE ON `discounts`
 FOR EACH ROW BEGIN

  UPDATE `users` SET `discount` = (SELECT SUM(`discount`) FROM `discounts` WHERE `user_id` = `OLD`.`user_id`) WHERE `id` = `OLD`.`user_id` LIMIT 1;
  
END

If I delete a record from the discounts table, the trigger fires
. If I delete a record from the coupons table, the records in the discounts table are deleted, but the trigger does not fire.
Why is that?

Answer 1

From documentation :

Triggers are not activated by foreign key actions.