Correcting each unwholesome habit is by no means easy — yet the effort must be made regardless. However much or little progress one is able to make, one must continue striving persistently, and in time all such habits will be fully corrected of their own accord.
Even the Lord Buddha himself, during the early lifetimes of his perfection of the virtues, still had knowledge and conduct that were lacking — as is common among all beings — and so he too stumbled and struggled along the way. In some lifetimes he was born as a tiger, an elephant, a deer, a barking deer — in short, in some lifetimes he was born as an animal, in others as a human being: sometimes as a person of poverty, sometimes as a king, sometimes as a scholar.
Yet however much he stumbled and struggled; he persisted in training himself throughout — as can be observed from the various Jātaka tales.
To declare oneself a Buddhist is to declare oneself a child of the Lord Buddha, and therefore to assume the duty of training oneself in his footsteps. Upon recognizing any unwholesome habit within oneself, one should hasten to correct it — compelling the mind against its inclination, doing so repeatedly and persistently, until familiarity with goodness is established before long.
From the book Buat Mai Sia Pha Lueang, Suek Mai Plueang Pha Lai (Ordained Without Wasting the Robe, Disrobed Without Squandering the Many Robes), page 63
