So many commentators did not live through post-USSR 90s to completely miss the mentality and culture which shapes Putin's decisions.

First, you need to understand values of a person, then their goals, then their methods to achieve the goals. 90s in post-USSR countries were a relatively free environment (from state prosecution) and it naturally selected for individuals which wanted as much power as possible and were willing to take it. For these individuals power is given only to those, who are powerful enough to have it, and must be taken from those, who are not powerful enough to keep it. If you are having your power, than it is moral for you to keep it until you don't.

This way of thinking is not something new or unique to post-USSR 90s - we as humanity have lived with this way of thinking for millennia and our thinking gave birth to countless empires and kingdoms. Those, who were powerful enough to be emperors, also had a right to be. Those, who challenged them in their power, would be new emperors, if proven powerful enough, otherwise would be painfully killed, their property and wives taken and their name forgotten. Let's call this mentality a "Cult of a Warrior". When you are living in this mentality, nothing is worse than feeling shame of abandoning your ideals or friends; you must be a truthful Warrior of the Cult until you die. But in the same time you can freely take anything you like which does not already belong to any of your friends, because if somebody is not powerful enough to fight you, than this person is not worthy of keeping this thing in the first place.

Some of us (humans) during a course of time have countlessly discovered and rediscovered that people can be treated as equal in principle, independent on their physical/economic/political power. This arrangement led to a more productive economic environment where zero-sum-game of Cult of a Warrior changed to a positive sum game of "Everybody Must Be Soft Cult". Also less overall human suffering is kind of cool, but economy thing is always first. In Everybody Must Be Soft Cult power over people can be used only with great care, everything is governed by a bureaucracy and no-one is unwilling to take too much responsibility for any action. This Cult uses a strong moral system to prohibit each of its members from using too much power on the others and those, who do not accept this system, are gradually punished with worse and worse strikes of punishment each time to learn their lesson. At the end, those individuals, who do not understand the reason for given punishment (its always abuse of power over others), are brought to death or exiled. Welcome to the Western civilization as we know it.

So let's go back to Putin and Ukraine. If we accept as an axiom that Putin is an adept of the Cult of a Warrior, then we can make the following conclusions:

1. Putin sees himself as a Chief Warrior of his tribe and therefore has factual and moral power to make any decisions for his tribe as he likes it. I will call him the "Chief Warrior" from now on.

2. The Chief Warrior sees that as time goes on, more and more fellow members of his tribe are turning from Cult of a Warrior to the Cult of Everybody Must Be Soft. From a point of view of a Warrior nothing is worse than to convert yourself to an Everybody Must Be Soft person. Worse is only when your children convert to Everybody Must Be Soft Cult and become all PC and LGBTQ drug loving hippies. No Warrior wants that to their children.

3. So from the Chief Warrior point of view he (in the Warrior cult its always he) does not have any choices at all regarding what to do with his life and how to guide his tribe next. First of all, he must save the tribe from this fucking Everybody Must Be Soft epidemy which is happening right now and must do so ASAP.

4. To save the tribe from Everybody Must Be Soft epidemy it must be separated from the source of the illness in the first place. That means economic and information blockade. All key technologies and industries must be developed in house, all external communication must be ceased, the nation must be quarantined until it find its Warrior soul again. Also its awesome if some of the most active bad blood from the Everybody Must Be Soft movement emigrates in the process.

5. So how to turn a course of a nation of 100+ million people, rapidly integrating from 1990s into Western economy and system of values? It is not so easy. You nee some help from your opponent in doing so. Remember Eastern martial arts - it takes less power to use your opponent against himself, then to do everything all by yourself? So you need to use Everybody Must Be Soft system of punishment to get yourself excluded and expulsed from its system. Economic sanctions is the name for it. For all sanctions the national economy will get a strong hit in the short term, but will become independent from the Everybody Must Be Soft economic system in the long term. Everything, which does not kill us, makes us stronger - said a fellow Warrior (or something like that) once.

6. How to get economic sanctions from the West? Everybody Must Be Soft always punishes for abuse of power, so we must show it to them. Crimea in 2014 was a nice start and we also reminded our fellow Warriors that our soul of the Warrior is not lost yet to the illness, that the times are turning. Also have to make internal reforms regarding freedom of speech, independent news media and political parties to smoke out all the Everybody Must Be Soft elite, so that this liberal pus comes out of an ill body of the Warrior which always has been and always will be Russian Empire, or Russia as it is simply called right now.

So what can people from Everybody Must Be Soft Cult can do to gain advantage in this fight? First of all, get their heads out of their arses and imagine that some people from another culture living on another continent might think differently than they are regarding fundamental ways of living and morality. Take some LSD and watch Chinese martial arts movies for Christs sake if you have so limited imagination.

Second, launch a program of giving free Western university education to Russians with a condition of returning back to their shitty dictatorial country as it is right now and starting improving something in this regard. Subsidize creation of Russian voice-over for all Western movies, give free English language classes to people over 30 and overall increase cultural transfer to people living currently in Russia. To kill Putin you have to convert all these people into the Everybody Must Be Soft mentality.

Third, in NO CASE create any new economic sanctions to Russia and repel all the old ones. Going the sanctions route would be like giving the Chief Warrior exactly what he wants on a silver plate. Give large amounts of aid to Ukraine to compensate for inconvenience of having a bully neighbor at the same time.

Fourth, either Everybody Must Be Soft Cult wins by converting everyone over, or it dies from hands of the Great Russian and Chinese Warriors who are getting stronger in the meantime.

PS. Sorry for my grammar and typos, not a native speaker.
Also slightly edited regarding grammar/typos.