Does Rhystic Study trigger if an opponent pays the one generic mana to avoid it?

Rhystic Study reads: "Whenever an opponent casts a spell, you may draw a card unless that player pays {1}." The key word here is unless — the ability only triggers and results in a card draw if the opponent does not pay the {1}. If they pay the mana, the trigger condition is never satisfied, and you draw nothing.

Under CR 603.1, triggered abilities trigger when their trigger condition is met. The trigger condition on Rhystic Study is implicitly "an opponent casts a spell and does not pay {1}." Because the payment is part of determining whether the trigger fires (or more precisely, whether it produces its effect), paying the cost completely avoids the draw.

In practice, the opponent is given the opportunity to pay {1} as the spell is cast and the triggered ability is being put on the stack. If they pay, the ability either does not trigger or is countered by its own condition — the result is the same: no card is drawn by the Rhystic Study controller.

Example: Your opponent casts Lightning Bolt and pays {1} in response to Rhystic Study's trigger. You do not draw a card. If they had cast Lightning Bolt without paying, you would draw one card.

Note: Rhystic Study does NOT trigger once and then get "countered" by payment in the traditional sense — the payment simply means the controller of Rhystic Study gets no card draw. There is no separate triggered ability to counter; the payment is built into the trigger's resolution condition.