Mao had a strong interest in the political system, encouraged by his father. His two most famous essays, both from 1937, 'On Contradiction' and 'On Practice', are concerned with the practical strategies of a revolutionary movement and stress the importance of practical, grassroots knowledge, obtained through experience. Both essays reflect the guerrilla roots of Maoism in the need to build up support in the countryside against a Japanese occupying force and emphasise the need to win over 'hearts and minds' through 'education'. The essays, reproduced later as part of the 'Red Book', warn against the behaviour of the blindfolded man trying to catch sparrows, and the 'Imperial envoy' descending from his carriage to 'spout opinions' .