Can automated update of a field trigger another rule?

Can automated update of a field trigger another rule?

..if the rules are for different modules? For example, when a task is completed the rule will tick a box in a potential card and it works. However, the other rule should be triggered by this update and send an email to the customer and it does not work. If I manually update the field, the rule is triggered but not if the other rule has updated the field. What am I missing here?