do by halves

verb1

1. •
   To perform (a task, etc) partially or incompletely; to do (something) inadequately, halfheartedly, or shoddily.

   • [A] pedestrian tour of Europe could not be complete without them. Of course that decided me at once to see them, for I never allow myself to do things by halves, or in a slurring, slipshod way. — 1880