Never was a technique so well named.
The setup is just as important in grappling as it is in striking. If you dive for an armbar with no setup, you won’t reap any rewards. In fact, you might even get yourself caught in a submission, just as in striking where charging forward can get you knocked out instantly.
However, the principle of setups is the same in both striking and grappling: distraction. One effective setup in striking is taking an angle. By taking an angle, your opponent must turn to face you. Thus, your opponent is momentarily blinded to your intentions because they are occupied.
How does this transfer to grappling? Simple. Breaking posture. Posture is one of the fundamentals of grappling. If your posture breaks, your opponent must spend the time to fix that leak.
In the below video, we observe a neat technique that breaks posture and then sweeps in some neat deception: