he cryptic film title is a reference to a scene (not included in the film) in the original book, where Begbie and Renton meet 'an auld drunkard' who turns out to be Begbie's estranged father, in the disused Leith Central railway station, which they are using as a toilet. He asks them if they are "trainspottin'."[31]
Irvine Welsh himself has explained in a Q&A that the title is also a reference to people thinking that the hobby of trainspotting makes no sense to non-participants. Likewise, the same applies to heroin addiction: to non-addicts the act seems completely pointless whereas, to someone hooked on heroin, it makes absolute sense.

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