it was that people who didn't know the option was even a thing wouldn't necessarily feel the option was missing from the game in the first place (since you can't miss something you never had.)
It isn't missing from the game. It's in the 5e DMG.
"SUCCESS AT A COST
Failure can be tough, but the agony is compounded when a character fails by the barest margin. When a character fails a roll by only 1 or 2, you can allow the character to succeed at the cost of a complication or hindrance. Such complications can run along any of the following lines:
• A character manages to get her sword past a
hobgoblin's defenses and turn a near miss into a hit,
but the hobgoblin twists its shield and disarms her.
• A character narrowly escapes the full brunt of a
fireball but ends up prone.
• A character fails to intimidate a kobold prisoner, but
the kobold reveals its secrets anyway while shrieking
at the top of its lungs, alerting other nearby monsters.
A character manages to finish an arduous climb to the
top of a cliff despite slipping, only to realize that the
rope on which his companions dangle below him is
close to breaking.
When you introduce costs such as these, try to make them obstacles and setbacks that change the nature of the adventuring situation. In exchange for success, players must consider new ways of facing the challenge. You can also use this technique when a character succeeds on a roll by hitting the DC exactly, complicating marginal success in interesting ways."