Stealth has many forms.
Camoflage, Misdirection, Obfuscation, Decoys, Traps.

All of them rely on the enemy being too complacent to monitor their surroundings.
70% of people fall for this. And because these fools don't think they should have to cover their backs as well as their fronts, these forms of combat tend to be nerfed quickly after release.

-From the victim's point of view they died either instantly, or very slowly but unable to act once caught in the trap. It is because of this aspect that the vocal minority scream for this form of combat to be nerfed.

-From the Aggressor's point of view however the combat started long before the victim was aware, carefully guiding the victim to the point of execution or simply evading line of sight. Putting in the time and the patience for the guaranteed kill.