You have missed the point (understandable as the conversation pivoted from how does it work to how is it coded)
Okay, maybe you mean "steps" in a coding sense, and maybe the conversation did "pivot" but in your earlier comment you were using the word "check" not "step":
What this means is that if they have 10% tenacity and you have 0% potency it is 90% likey the debuf WILL be applied on first check, but there is a second check as all debuffs have a 15% chance to be resisted. Many people assume if the tenacity is higher than the potency it will not apply , this is not the case. There is also a second check ,
If you really mean coding steps and not separate checks, then you should probably go back and edit this comment so that you don't confuse people. There is no second check.