Background: Revolver is the seventh studio album by the English rock band the Beatles. Released on 5 August 1966, it was the Beatles' final recording project before their retirement as live performers and marked the group's most overt use of studio technology up to that time, building on the advances of their 1965 release Rubber Soul. The album's diverse sounds include tape loops and backwards recordings on the psychedelic "Tomorrow Never Knows", a classical string octet on "Eleanor Rigby", and Indian-music backing on "Love You To".
Context: In December 1965, the Beatles' Rubber Soul album was released to wide critical acclaim. According to author David Howard, the limits of pop music "had been raised into the stratosphere" by the release, resulting in a shift in focus away from singles to creating albums of consistently high quality. The following January, the Beatles carried out overdubs on live recordings taken from their 1965 US tour, for inclusion in the concert film The Beatles at Shea Stadium. The group's manager, Brian Epstein, had intended that 1966 would then follow the pattern of the previous two years, in terms of the band making a feature film and an accompanying album, followed by concert tours during the summer months. After the Beatles vetoed the proposed film project, the time allocated for filming became a three-month period free of professional engagements. This was the longest period the band members had experienced outside the group collective since 1962, and gave them an unprecedented amount of time to prepare for a new album. Writing in The Beatles Forever, Nicholas Schaffner cites 1966 as the start of the band's "'psychedelic' period" and adds: "That adjective implies not only the influence of certain mind-altering chemicals, but also the freewheeling spectrum of wide-ranging colors that their new music seemed to evoke." Music journalist Carol Clerk describes Revolver as having been "decisively informed by acid", following John Lennon and George Harrison's continued experimentation with the drug LSD since the spring of 1965. Through these shared experiences, the two musicians developed a fascination for Eastern philosophical concepts, particularly regarding the illusory nature of human existence. Despite his bandmates' urging, after Ringo Starr had also partaken of the drug, Paul McCartney refused to try LSD. As reflected in the more conventional subject matter of his lyrics on Revolver, relative to those of Lennon and Harrison, McCartney drew his inspiration from the intellectual stimulation he experienced among London's arts scene, particularly its thriving avant-garde community. While arranging dates for the band's world tour, Epstein agreed to a proposal by journalist Maureen Cleave for the Beatles to be interviewed separately for a series of articles that would run in London's Evening Standard newspaper in March 1966. Cleave's observations reflected the band members' more sophisticated personalities beyond the simplistic portrayals that were commonplace at the time. Of the two principal songwriters, she found Lennon to be intuitive, lazy and dissatisfied with fame and his surroundings in the Surrey countryside, while McCartney conveyed confidence and a hunger for knowledge and new creative possibilities. In his book Revolver: How the Beatles Reimagined Rock 'n' Roll, Robert Rodriguez writes that, whereas Lennon had been the Beatles' dominant creative force before Revolver, McCartney now attained an approximately equal position with him. In a further development, Harrison's interest in the music and culture of India, and his study of the Indian sitar, had inspired him as a composer. According to author Ian Inglis, Revolver is widely viewed as "the album on which Harrison came of age as a songwriter". CANNOTANSWER
Question: why did he refuse?

Answer:

CANNOTANSWER