Ask HN: How to stop being a worrier? 8 years ago
You should study math. Especially, the problems in discrete math. These problems often require you consider "every single situation", "all scenarios" and "all of the 27 possible outcomes" and likely go way above and beyond that.
As a bonus, math trains mental endurance, toughness, agility and creativity. Ain't nothing compares to math in this department.