one-track mind

one-track mind idiom
A mind limited to only one line of thought or action, as in All you think about is sex—you have a one-track mind. This expression, alluding to a train that runs only on one track or in one direction, was first recorded in 1928.

The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

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