Past tense of sidetrack, meaning to be diverted from a main purpose or course of action. To be distracted or led away from the original focus.
From railroad terminology, where a sidetrack is a short section of track connected to a main line. The metaphorical sense of being diverted from one's main course developed in the late 19th century alongside railroad expansion.
The railroad origin of 'sidetracked' is still visible in the phrase 'getting back on track.' Train metaphors permeate our language about focus and direction because railroads were the first technology that demanded absolute adherence to predetermined paths.
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