Comment by summa_tech

Unfortunately, the symmetry provided by higher levels of your software stack is not always reflected by the lower levels. This causes your symmetry to be created as an abstraction. (Subroutines are more efficient to implement than co-routines on real hardware.) Abstractions are leaky and this, in turn, causes the superficial symmetry to merely mask the underlying asymmetry.

If done exceptionally well, the only visible evidence of the leak will be substantial performance disparities between seemingly symmetric features (well done! this is unusual).

If done with the normal level of software design quality, the evidence will show up as quirky behavior, imperfect symmetry, "well this one always works but the other one is not reentrant", etc.