In the two years that Ukraine has been fighting off a Russian invasion we never got as close as we did yesterday to a NATO country leader being killed by a Russian airstrike. If this had happened the events that would have transpired would have been nothing less than catastrophic for the world as a whole.
If you did not know Greece's Prime Minister was visiting Ukraine's southern city of Odessa with the President of Ukraine. When leaders from other countries have traveled into Russia it has been common for Russia to be warned through back channels to prevent an incident from occurring.
Why do this? Well, it is pretty simple as both sides do not want to get into direct conflict with each other no matter what they say publically. If a NATO country has important government officials get killed or injured the fallout would be catastrophic because of NATO's Article 5 mechanism. This allows a country to calls for the other member countries to come to its aid and that would cause a NATO mobilization against Russia resulting in direct and clear action.
Sadly the result of this would be nothing short of an all out war with Russia which would result in not only unfathomable deaths and suffering but quite possibly the end of the world as we know it due to nuclear weapons. Luckily that did not happen and everyone ended up safe but the reports state the missle hit within 200 meters (roughly 600ft) of the convory carrying the Prime Minister of Greece.