What is the theme in The Life and Opinions of Tristram Shandy by Laurence Sterne?

Tristram mentions hobby horses at the beginning of the first volume, and it remains a constant thread throughout. Most notably his Uncle Toby rediscovers his health and love for life through his hobby of reenacting battle scenes. This proves the emphasis Tristram places on hobbies. In fact, without a hobby to occupy a person, Tristram suggests a person only spends their time thinking about the negative aspects of life. For example, Tristram's father only gets over his eldest son's death through his hobby of philosophizing and putting theories into a book that is intended to educate Tristram.