"The man who never alters his opinions is like standing water, and breeds reptiles of the mind"

This quote by William Blake is a warning against complacency and a pointer to keep an open mind. It suggests that when an individual never ever changes their viewpoints, they become stagnant and their thoughts end up being stagnant also. This stagnancy can result in the growth of unfavorable and hazardous thoughts, which Blake describes as "reptiles of the mind". In other words, if a person never challenges their own beliefs, they can become susceptible to negative and harmful ideas. This quote is a tip to stay unbiased and to challenge our own beliefs in order to prevent the development of these "reptiles of the mind". It is a pointer to keep our minds active and to be going to change our viewpoints when needed.