4 unfit subjects

The Four subjects not fit for speculative thought:

1. The specific qualities of a Buddha

2. A person’s jhana attainment

3. The results of kamma

4. The nature of the world

Anguttara Nikaya 4.77

(Speculating on these could lead one to mental distress and insanity.)

References

• The Complete Book of Buddha's Lists -- Explained. David N. Snyder, Ph.D., 2006.
• http://www.thedhamma.com/