A.e. Waite 
The Alchemical knowledge of Paracelsus [EPUB ebook] 

All the fault and cause of difficulty in Alchemy, whereby very many persons are reduced to poverty, and others labour in vain, is wholly and solely lack of skill in the operator, and the defect or excess of materials, whether in quantity or quality, whence it ensues that, in the course of operation, things are wasted or reduced to nothing. If the true process shall have been found, the substance itself while transmuting approaches daily more and more towards perfection. The straight road is easy, but it is found by very few.