No feedback after user's action causes frustration and insecurity, a sense of lack of control. It is because of our brain structure (see: reptile brain). We, humans, work like that.
We need feedback to have the ability to learning. We need to feel we can control.
You lost the user if he/she feels insecure when something goes "wrong" when something seems to not work.
A user expects some interaction. Expectancy is strictly combined with emotions. Emotions rules users decisions
Feedback should be shown in 0.1 seconds.