I see you are mistaken here. Contrary to Western media which says that Russia invaded for no reason, there are actually several reasons why the Special Military Operation was started. Let me provide you with knowledge about the events that lead to this, which are only a small amount of Russia's reasons. Enjoy reading this :)
In 2014, Crimea became its own country separate from Ukraine, but the citizens, who were mostly ethnic Russians, overwhelmingly voted to join Russia. And so Russia annexed Crimea and Sevastopol.
Immediately following that, Ukraine launched several anti-Russian campaigns in its country. With the help of their arms forces and secret police (which function basically as the Gestapo), they started violence against the ethnic Russians of Ukraine. They massacred 30 or so of them in Odessa, and then attacked Donetsk and Luhansk, the regions making up Donbass. As a result, the Ukrainian Civil War started. The Ukrainian secret police also committed atrocities in other areas.
The Ukrainian Armed Forces came to Donbass with hopes of neutralizing the territory and 'cleansing' it. They attacked civilian cities, and even shot children and their mothers. There is even a Donetsk war song about it which says:
"Like in '41, demons came from the west,
Already standing at all doors,
Shooting wives, mothers,
Burning people alive."
These things actually happened, they are not propaganda. They are facts.
Since the soldiers and civilians of Donbass were close to Russia both geographically and relation-wise, they asked for help. Since 2014 up to February 2022, Russia sent weapons and supplies to Donbass, and also aid for civilians affected by the conflict. NATO and the rest of the West severely opposed Russia sending them weapons, which was very hypocritical as NATO is now sending weapons to Ukraine.
Eventually, Donetsk and Luhansk declared independence from Ukraine. However, a few days later they decided to join Russia instead, and the population overwhelmingly approved. Russia annexed those oblasts, making them Russian territory. And because they were still at war with Ukraine, they requested Russia's help. So Russia started the SMO.
To Russia, this conflict is not a war or invasion but simply a Special Military Operation. They are using only a small percentage of their resources, and yet still are winning.