Effectiveness is about
doing the right task, completing activities and achieving goals
Efficiency is about
doing things in an optimal way, for example doing it the fastest or in the least expensive way. It could be the wrong thing, but it was done optimally
Before you try to be more efficient
first try to be more effective
If one of you decides to build a tower, will he not first sit down and
calculate the outlay to see if he has enough money to complete the project? He will do that for fear of laying the foundation and then not being able to complete the work.
—Luke