You must proclaimed it before all others or when no one else has for X amount of time (24 hours as an example) in this honor bound and/or evidence based system.
This claim can only be made on one position/object at a time and any additional claims made by one person nullifies the most previous and past claims of that one person.
Touching and/or leaving this position/object without restating king's ax constitutes relinquishing all claims on said position/object.
Similar to calling shotgun, dibs, bagsy, or not it.
Roots may be in the social order and customs of Medieval times. Or my mom made it up, idk.