A 'Virtuous cycle' is created by the educated parents when they invest heavily in the education and skill training of their children because these children when they become parents, will also invest heavily in the education and skill training of their children, as they realise the importance of education.
This cycle will continue to repeat for generations, thus creating a virtuous cycle'. In contrast, uneducated parents, not realising the importance of education, do not invest in their children's education, thus, creating a 'vicious cycle'.