The antonyms for "leaving undone" would be "accomplishing," "completing," and "finishing." These terms refer to the act of carrying out a task until it is done in its entirety, leaving nothing left to do. By accomplishing a task, one ensures that it is done correctly, efficiently, and thoroughly. It is said that completing a task brings a sense of satisfaction and accomplishment, which is lacking when leaving things undone. In conclusion, it is always better to accomplish or complete a task than leaving it undone, as it can have adverse effects on productivity and morale.