(CNN) The fact that nobody really knows what's going to happen next in Ukraine is the entire point. It is the core of Russia's strategy.

It has been for the four years of the war, and we should by now have stopped acting surprised by Russian pragmatism and adventurism. It's almost impossible to predict this accurately.

Five basics explain how the situation got to where it is now and how it's hard to know where it goes next.

First is that this is not a new war. It's not even an uptick of violence in the war. Fighting has persisted since the so-called Minsk accords of 2015. Shelling has happened almost daily along the frontline between Ukraine proper and the separatist areas of the Donbass -- and happened before and after the Kerch incident at the same rate.

People have died on both sides every week. The world simply didn't pay attention until the Russian military made the drastic step of overtly confronting the Ukrainian navy on Sunday. This is important to understand, as it explains why flare-ups like the Kerch Strait can turn into full-scale warfare in days, because both sides are armed, are ready for conflict, and have residual pools of loathing built up over 50+ months of fighting.

Second is that the Russian strategy is based on masking their moves and keeping their opponent off-balance. Russian military drills along the southern border happen now with sufficient regularity that it's hard for Western observers to work out what's a lurch toward war and what's just training.

The Russians have slowly been sending supplies into Eastern Ukraine -- the Donetsk's People's Republic (DNR) -- for years now. The leader of the DNR, Alexander Zakharchenko, was killed in a bomb blast a few months ago, leading many analysts to remind us that the swift departure of separatist leaders has occurred in the past before upticks in activity in the war. But even that is not a pattern that makes this predictable.

Western intelligence assessments of Russian President Vladimir Putin see him not as the master long-term strategist, but as the ultimate pragmatist and opportunist. He sees what he can get away with and then does a little more or doesn't.

The analogy of Putin as the geopolitical student of judo -- his favorite sport -- is tired, but apt. He sees what his opponent has overlooked -- or doesn't care about -- and exploits it. Only this fight is about sovereignty in the European mainland, not two sweaty men in robes.

Third is that Ukrainian President Petro Poroshenko doesn't have a strategy, and frankly it's hard to see how someone in his position could.

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This has long ailed Ukraine. It is the malaise of power in Kiev: Corruption; oligarchy; under-resourced forces; infighting in a tired elite. All of it has hamstrung Ukraine's response to repeated Russian invasions.

If you need a sign of how small and internecine the political hierarchy here is, remember that Poroshenko is behind in the polls for the March presidential elections to Yulia Tymoshenko. She was a key figure in the anti-Russian-influence protests of 2004, known as the Orange Revolution. It's the same faces, often with the same old problems.

The job of Ukrainian president is not enviable. It is about managing a slow bleed. Moscow wants to retain influence on your nation, or at the least make it so weak it cannot ever imagine joining NATO or the EU. NATO and the EU want you to resist this, but have absolutely no intention of setting red lines deep enough that they end up sending troops to fight in your defense.

Internally, your public is increasingly furious with the destructive mess and slow harvesting of your territory by Russia. And your armed forces simply can't modernize fast enough to be a genuine match for Moscow's.

Even Wednesday's introduction of martial law was desperately confusing in practical application: are Russian citizens banned from entering Ukraine? Will there be a blockade on separatist areas? What does martial law look like and what does it change? If you do nothing, do you further provoke Russia, or do you actually provoke Russia if you do something?

Few people know and as I write this, two hours in, it's still unclear what martial law has changed. It seems that as Ukraine's president, whatever you do, you lose.

Fourth is that Putin really needs this. If you ever wonder why the Russian leader would go to all this trouble, recall that this is in his DNA.

The collapse of the Soviet Union was to him the "greatest political catastrophe of the 20th century," not an inevitable twist of economics. Russia has been involved in US elections -- and perhaps in Brexit, Hungary, Syria, Libya, Afghanistan, Africa, spy poisonings in Salisbury, espionage attempts in the OPCW, all since 2016. They show that Putin wants to restore the outsized global reach that the dwindling Soviet economy had during the Cold War. This is about prestige and vengeance. About restoring former glory. And he doesn't have term limits, or a legislative or judiciary, holding him back.

Finally -- and this is the big one that could have people really worried -- is US President Donald Trump.

Former US President Barack Obama refused to send combat troops or risk military engagement in Ukraine. But he got the world behind sanctions and led the charge of fierce condemnation at a time when many European states actually could have done without the headache of worsening ties to Moscow.

Obama's line was not militaristic, but it was firm and it damaged the Russian economy -- and with it, Putin's standing. Now, Moscow makes the brazen move of an avoidable yet open military-on-military attack in the Azov Sea -- rather than using proxy separatists or guises -- and the White House is muted on the issue.

Trump spoke out against "aggression," said he was "not happy" and might cancel a meeting with Putin. Yet remarkably the meeting was not outright canceled as a matter of course, and is still on the table days after the Kerch incident. In fact, his national security adviser John Bolton seemed keener to confirm it than condemn Russian actions, and omitted Ukraine from the list of things the two men would discuss. When asked about Ukraine, Bolton pointed reporters back to the recent statement of UN Ambassador Nikki Haley. There appears to be a strange phobia of outspoken criticism of Moscow from inside the grounds of the White House -- like stern words against Putin might result in anaphylactic shock. And Trump's unhappiness extends "either way" -- suggesting he could hold both Ukraine and Russia responsible. When Putin evaluates the global signals, assesses how far he has gone and how much further he might go, this is the key variable in his mind.

And then, you can be sure, the Russians will do exactly the opposite of what seemed inevitable, and wait. Or act suddenly. The inability to predict their next move is the point.