But I wondered can any buddhist theory or practice can ever be harmful to a human?
Many people pratice certain techniques as Buddhist pratice. When you come across a pratice that someone says is a Buddhist pratice you should try to ascertain:
- is this actually the Buddhist pratice comparing it with the original words of the Buddha in record or have you learned the right things
- have you understood the pratice correctly and to the enough detail or do you understand the theory behind the pratice well enough
- is what you are practicing the correct pratice or despite you have learned the right thing and know the theory are you putting it to practice the proper way
- does your pratice fit your character type. Now within the the different meditation techniques there are suitability based on character type.
If any of the above are not met you cannot blame the pratice.
Also if you pratice Insight meditation then nothing can go wrong. More particularly you should contemplate on the arising and passing of sensations pertaining to:
- Sensation from beauty or ugliness of physical form and sensations arising from the states of material form
- Sensation on their own right due to perceiving something is favorable or not
- Sensation due to mental states
- Sensations due to mental content
One case of Zen Sickness (Zen Sickness by zen master Hakuin) mentions about excessive striving. In Buddhism you effort should be balanced. Excessive striving can lead to craving, restlessness and doubt:
- you are caving for the result or some experience which you are chasing after through meditation. You are accumulating craving instead of reducing it.
- you are too frequently measuring your progress hence restless about getting the results fast or doubting the technique, the teacher, and your ability. Resentment follows if it is less and excessive pleasure if it is more. Also you are doing something other than meditation which is measuring progress. Also if measuring lead to doubt you are engrossed in doubting that practicing.