Why is it so difficult to be virtuous?

According to Aristotle, it is difficult to ,be virtuous if you aren't in the habit of being virtuous. He notes that if you aren't virtuous, vice is a source of pleasure, but if you are virtuous, vice is a source of pain. Thus, the more virtuous you are, the easier it is to be virtuous.

“We must take as a sign of states of character the pleasure or pain that ensues on acts; for the man who abstains from bodily pleasures and delights in this very fact is temperate, while the man who is annoyed at it is self-indulgent, and he who stands his ground against things that are terrible and delights in this or at least is not pained is brave, while the man who is pained is a coward. For moral excellence is concerned with pleasures and pains; it is on account of the pleasure that we do bad things, and on account of the pain that we abstain from noble ones.”