If you've reviewed an item on Someday/Maybe many times and each time you've
decided not to do it that week, then in future reviews, because of habit,
it's then easier to decide again not to do it and harder to decide to do it.
This is one reason I think it's a good idea to separate the Someday/Maybe list
into lists to be reviewed more often and less often. That way, something you
want to do sometime in the next few years doesn't get tarnished by large
numbers of reviews and rejections before you actually face doing it.
Inability is an abstract thing involving comparison with alternate universes; it cannot be experienced.