The whole point of abstraction is to replace the need of understanding all the details of the implementation with a more general and simpler concept. So while the abstraction itself may have a non zero cognitive cost for the end user, this cost should be lower than the cognitive cost of the full implementation that the abstraction hides. Hence the net cognitive cost of proper abstraction is negative.

Abstractions allow systems to scale. Without them, it would be impossible to work on a system that's 1M lines of code long, because you'd have to read and understand all 1M lines before doing anything.