Some of the reasons why a Manager gets stressed are:

The job delegated to the subordinate is not completed in time and the productivity is not up to the expectation. In most cases we blame the subordinates. One of the main reasons for not getting the desired result is the lack of people skill or dealing with the emotions.
If you don’t have good relationship with the people with whom you want to keep, you will not feel good and you may go under mental depressions.
If I don’t have good relationship with my wife, the main reason may be the way I communicate, she does not like. Same reason applies to all other people also, let it be subordinate, boss, children and friends.
People say that they are getting struck due to work pressure. Tell me how the statement is justifiable? Stress is mental. If you work more you will get tired that is physical. But stress is mental. If you are playing a game and if you put 100% of your effort in the game, you will get tired and you get a nice sleep at the end of the day. If you can handle any kind of situation and any person you will start enjoying.
Most of the above concerns are discussed in the previous chapters.
In a nutshell reasons for stress are:
Expectation: Expect least from others, do whatever you can do from your side.
Competing with someone: Compete with yourself.
Not accepting the present moment: Living in the past or future3.
Not able to deal with own emotion and other’s emotion.
Not having enough knowledge of human psychology ( Self & others )
Not able to keep up with timings and commitments6.
Lack of physical exercise: Include physical exercise: Yoga, Jogging, Walking, Skipping
Not showing gratitude to others ( Ego)
9.Not able to forgive self & others
If you can deal with and overcome the above factors you can lead a happy and peaceful life.