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Begbie always constructed imaginary qualities in his friends, then shamelessly claimed them for himself.
— Irvine Welsh • Trainspotting

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
Begbie is described as inventing qualities in his friends and then claiming those inventions for himself. The double move makes his self-presentation especially hollow: even the borrowed traits were made up. The word shamelessly gives the observation a sharp, openly critical edge.
Context reviewed