We mistakingly adorn most that part of life which least requires it, and neglect to provide for that which will want it most.
Karasowski says mistakingly that the movement referred to is the Adagio of the E minor Concerto.
When it is placed ultimately upon a forbidden object: as to hope for some evil to yourselves which you mistakingly think is good.
1630s, from mistake (v.). Meaning "unintended pregnancy" is from 1957.