Stress, mental tension results from wanting reality different from what it is. You can see this easily in your own mind. Whenever you sense conflict, tension or stress of any kind, observe carefully:
What seems to be happening – your mental creation or projection
What is really happening.
Remember that if you believe you know what is really happening then that is a further mental creation. So what is really happening, if not that also? As you continue this process, it becomes clearer that what is really happening remains unknown. If it was known, that would be yet another mental creation and not reality.
Observe these two carefully: what seems to be happening and what is actually happening. As they begin to separate in your mind, the what seems to be happening ceases to disturb you since it is unreal. And the reality ceases to disturb you since you do not know what it is.
As long as you are fully connected to reality there can be no stress or mental tension.