Getting better at tango often means being careful with how much effort we exert. If we're in the beginning stages of learning, it's understandable to want to put forth a lot of physical exertion (leading with arms, anticipating while following, etc).
Although it's true that tango requires effort, the majority of our energy should be directed towards other areas: How much physical effort do we give our partners so they feel our connection, but not so much that we're knocking each other off axis? How much (or little) energy should we put into keeping our frame so that we have a solid presence, but not to the point where we feel tension...or feel too loose? Are we putting enough energy into finding our balance, or just falling into every step?
The concept of effort in tango shouldn't be associated only with physical force. It's more helpful to think about effort in terms of control. But let's not take that to mean we must control the entire dance. As one half of the tango partnership, we're always trusting 50% of the outcome to another person. That being said, what we're left with is a large amount of - and need for - self-control.