"individual's perception of how easy or hard it is to enact a specific behavior" is directly from this nature artical ( https://www.nature.com/articles/s41599-023-01724-9#:~:text=Perceived%20behavioral%20control%20is%20defined,experience%2C%20resources%2C%20and%20capabilities. )
The definition in this card is directly from the 300 page document, and it a little round about. There are other definitions that also seem to be more direct, like the one from upenn "The extent to which a person feels able to enact the behavior" ( https://www.med.upenn.edu/hbhe4/part2-ch4-theory-of-planned-behavior.shtml#:~:text=Perceived%20power-,Perceived%20behavioral%20control,and%20perceived%20power%20with%20beliefs ).