It's important to remember 3 things:
1) at no point was Napoleon's intent to conquer or annex Russia.
2) he didn't even plan to go into Russia proper, his intention was to force a decisive battle in NE Poland/Lithuania or at worst Belarus, and the objective was to force Akeksander to not violate the treaty he'd agreed to the last time Napoleon had fought a decisive battle against him.
Which brings me to 3) re: his terminal egomania, you need to remember the pattern;
1) France's UN-monarchy constitutes existential threat to surrounding states, who almost universally support it's terminal nation.
2) A surrounded Napoleon fights to prevent 1, somehow wins, and treaties are agreed upon.
3) As soon as they can, usually meaning as soon as Britain can fund enough of them to again surround France with a Coalition, the monarchies violate the treaties and invade/try to invade France.
4) repeat steps 2/3 ad infinitum.
It had become that, at least so long as he could not invade Britain and therefore break their bank, there was never going to be a permanent peace. The existence of France itself was a constant threat to monarchies worried it would inspire similar movements in their nations. In many cases it did. So what, exactly, was Napoleon supposed to do? His thinking was always along the lines of problem-solving, and IMO his coronation and appointment of familial potentates was simply one way to try and resolve the inherent casus belli his government represented to its neighbours while trying to preserve what he thought were the essentials of the revolution.
We see that in the brief periods of peace his victories afforded, unlike a Hitler or Alexander or w/e with whom he is concerned, he did not bide his time building up the military and when ready, attack. Rather he'd immediately focus his attention on domestic concerns like the Civil Code, sanitation, education, law, etc. Especially towards the end, he was exhausted with war...he knew his talent at war was the key to his power and France's security, but he absolutely did not want war, nor fought for conquest. He'd fight in defense, to force peace. He was not annexing huge swaths of land or w/e.
Portrayed as a war-monger by his enemies, it's interesting to note how many times he actually declared war rather than the reverse.
His Russian campaign was a failure along many lines...IMO most notably he fell victim to strategic tunnel vision once the Russians slipped his grasp early on (horrible subordinate fuck-up, btw) and I think Borodino is by far his...laziest? Most brutal? Most selfish? Most exhausted?...worst battle ever by far. But the 2 failures he's most often credited with, ie wanting to vaingloriously conquer Russia and fighting the Russian winter are misplaced. He wanted Aleksander to abide by their alliance/treaty re:Continental system, not French Russia, and there was no precedent for the scorched earth Russian withdrawal that took place...it wasn't even a Russian strategy, it kinda evolved as it went along, amidst much argument in the Russian high command. He maybe stayed in Moscow too long, too. That'scat least where he later thinks his mistake was made. And btw, the Russian summer had about as much effect as the winter.
In my own view it was not one moment...it was that once his decisive battle was avoided early on, he kept pushing for it, thinking maybe today, maybe tomorrow. It was reasonable to expect that at some point the czar would have to fight or lose political agency...and in fact that proved true. But by then I think he'd acquired tunnel vision and wasn't himself. Some of his generals did advocate turning back to Vilnius or his planned winter quarters at Smolensk, so it wasn't impossible to see.