Complacence vs Complacency

When does one use complacence, and when does one use complacency? Both of them are nouns, so obviously they have different meanings and usage.

Complacence is a calm satisfaction with oneself. A monk is likely to be someone with a sense of complacence, at peace with oneself and with his lot in life.

Complacency is a whole lot more dangerous - complacency means a self-satisfaction but coupled with a lack of awareness of what is happening around it. It is normally used to describe a person or nation which has become so self-absorbed and satisfied that it does not see looming danger until it is too late. A champion swimmer who has a sense of complacency is unlikely to put in the effort to train, until his young upstart takes the medal from him.

So there you are, some tips from your friendly neighbourhood English teacher.