Immature sentimentality is generated by one's indulgence.

Somebody or something irritates you and you lose temper.

The heroine of the story cries and you cry with her.

You see somebody in a wretched condition and get emotional.

Something challenges you and you get defensive.

Somebody threatens you and you get aggressive.

You are being sentimental. Anybody can make you dance to his own tune. Are you a puppet? This immature sentimentality turns you into a puppet.

The human alternative is being passionate; thereby creating your own tune to dance to. Sentiments utilize the same energy which lies in the depth of passion.