39  [Comment to Article 10.2.1.1: While it is theoretically possible for an Athlete or other Person to establish that the anti -doping rule vi olation was not  intentional without showing how the Prohibited Substance entered one’s system, it is highly unlikely that in a doping case un der Article 2.1 an Athlete will be successful in proving that the Athlete acted unintentionally without establishin g the source of  the Prohibited Substance.]