The psychology of worry is by no means simple. I have spoken already of mental discipline, namely the habit of thinking of things at the right time.
 Bertrand Russell, The Conquest of Happiness (1930). copy citation

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Author Bertrand Russell
Source The Conquest of Happiness
Topic thinking psychology
Date 1930
Language English
Reference
Note
Weblink http://russell-j.com/beginner/COH-TEXT.HTM

Context

“Of course, the trouble may be fear of bankruptcy, and in that case his work is directly connected with his worry, but even then worry is likely to lead him to work so long that his judgement becomes clouded and bankruptcy comes sooner than if he worked less. In every case it is the emotional trouble, not the work, that causes the breakdown.
The psychology of worry is by no means simple. I have spoken already of mental discipline, namely the habit of thinking of things at the right time. This has ‘its importance, first because it makes it possible to get through the day’s work with less expenditure of thought, secondly because it affords a cure for insomnia, and thirdly because it promotes efficiency and wisdom in decisions.” source