From Ramana maharishi
Q. Why is it that the mind cannot be turned inward in spite of repeated attempts?
A. It is done by abhyas [practice] and vairagya [dispassion] and that succeeds only slowly. The mind having been so long used to go outwards, is not easily turned inwards. A cow accustomed to graze thievishly on others’ estates, is not easily confined to its shed. However, its keeper tempts it with luscious grass and fine fodder. It refuses the first time; then it takes a bit, but its innate tendency to stray asserts itself and it slips away. On being repeatedly tempted by the owner, it accustoms itself to the stall; finally even if let loose, it would not stray. Similarly with the mind. If once it finds its happiness within, it will not dwell outward.
(Bhagavan Sri Ramana in ‘Conscious Immortality’, ch. 4 [also “Talks”: 213])
Bhavin