The reason why purity ([0]) falls flat is because the pure approach only handles 90% of the problems efficiently. The remaining 10% will take more effort so you do not actually see a 90% reduction in cognitive burden but perhaps a 70% reduction. If there is an escape hatch for the remaining 10% of problems the cognitive burden would be reduced by the full 90%. But purists don't like escape hatches, because they think all the benefits of purity are gone, because it's an all or nothing thing (it isn't).
[0] It doesn't really matter what type of purity we are talking about here. Whether it's about pure functions as in FP or Rust code that never depends on unsafe code.
[0] It doesn't really matter what type of purity we are talking about here. Whether it's about pure functions as in FP or Rust code that never depends on unsafe code.