I often get confused between the definitions of the following 2 terms and when to use them:
Efficacy = capacity to produce an effect; effectiveness of something; doing the right thing.
Efficiency = extent/amount of time or effort used for an intended task or purpose; competency in something; doing things right.
e.g. (?) = The efficiency of my blog writing is lacking, and so is its efficacy.
Yep. I just confused myself a bit more.