I think you may be misreading him, Chesterton isn't saying you should stop improving yourself, but that you can't hope to find that improvement in a book detail

I think you may be misreading him, Chesterton isn't saying you should stop improving yourself, but that you can't hope to find that improvement in a book detailing the supposed habits of the wealthy and successful (or the one weird trick that makes everyone a millionaire). Your goal shouldn't be to become Cornelius Vanderbilt, it should be to take advantage of your abilities and circumstances to find your own path to success.