digress

(verb) lose clarity or turn aside especially from the main subject of attention or course of argument in writing, thinking, or speaking. Synonyms: stray, divagate, wander. Examples: "She always digresses when telling a story." "Her mind wanders." "Don't digress when you give a lecture."

(verb) wander from a direct or straight course. Synonyms: sidetrack, depart, straggle.