 During the same month that " Eight Miles High " was released as a single , the Byrds ' main songwriter , Gene Clark , left the band . His fear of flying was stated as the official reason for his departure , but other factors , including his tendency toward anxiety and paranoia , as well as his increasing isolation within the group , were also at work . Following the release of " Eight Miles High " and Clark 's departure , the Byrds never again managed to place a single in the Billboard Top 20 . 
