LUHE: Read about Russian politics. Kasparovs book is a good place to start.
Optics about Putin are very important internally in Russia. He has to be seen as a strong man and this image is very well controlled in a number of ways in the propaganda.
It sounds retarded, but it makes sense of many things Putin is doing. For instance, that is why he always leaves leaders waiting for him if at all possible. That is why he has the particular body language he has.
Putin has an ongoing campaign of aggression against the west and he has so far come out on top again and again (paradoxically, that he wagers this campaign is a sign of weakness: he needs victories abroad).
What can be done to stop Putin is to ensure that the consequences of this campaign outweigh the benefits. In other words, he must be made to look weak or risk being made to look weak. That is being accomplished with the sanctions (which he can't do anything about) and by credible threats of losing or being forced into concessions.
If Putin is given Crimea now against lifting sanctions, why not continue with Donbass? Why do anything different in Europe? Because he promised not to? There would be no incentive for him to do so.
This approach, make Putin promise (sort of) something and believe he will keep it, is the approach Bush and in particular Obama took with Putin. In reality, Putin computes the cost/benefits and do what seems best.