Shows a lack of self control

That implies that the inverse, bottling up your feelings, demonstrates self-control, and that self-control is always a desirable trait.

I disagree with both. Expressing your feelings is a part of good communication, and feeling free to express sadness or frustration as needed is how you stave off the kinds of arguments and blowups that have much more severe consequences.

Moderating your own behavior is about being cognizant of your emotions and the associated causes/effects, not ignoring them.

Why would self control require pretending you don't have emotions? If you are being aggressive, then yes, you are lacking self control.

But that is act, not emotion.

Self control is assimilating those emotions in a healthy way to understand the root cause rather than letting them overflow from mental->physical in inappropriate settings.

This is a cornerstone of Cognitive Behavioral Therapy, which is, in short, "I am free to notice that when this happens, I feel this certain way, and that usually relates to these outcomes. How can my behavior influence this in my favor?"

Cognitive Behavioral Therapy is not trying to teach you to hide all emotions the way comment I reacted to suggested. You being visibly sad is fine result. There is big gap between overflow and notion that "you are allowed to show feelings" is something bad.