observance vs thoughtlessness

observance

noun
  • The practice of complying with a law, custom, command or rule. 

  • That which is to be observed. 

  • Observation or the act of watching. 

  • A rule governing a religious order, especially in the Roman Catholic church. 

  • The custom of celebrating a holiday or similar occasion. 

  • Reverence; homage. 

thoughtlessness

noun
  • heedless disregard for the consequences of one's actions 

  • disregard for other's feelings 

How often have the words observance and thoughtlessness occurred in a corpus of books? (source: Google Ngram Viewer )