The discerning man straightens his mind, which is fickle and unsteady, difficult to guard and restrain, as the skilled Fletcher straightens the shaft (of the arrow).
That is from Dharmmapada, a buddhist work.
Subconscious mind apart form the programmed activities such as breathing, digestion etc, observes the activities of conscious mind and follows it when the conscious mind is not active or at rest.
If we (Servant) train ourselves to follow the heart (illogical mind), we don’t tend to do things in a disciplined way. But, the logical mind commands us to follow the disciplined way. The Logical ruler should be in command so that the illogical ruler would be dormant and the servant mind follows what the logical ruler commands. And thus Straightening the mind would be making the logical ruler in command and bringing the illogical mind in control.