I started a little run in Crusader Kings II. And lost track of the hours in a highly irresponsive manner.
I started as a double county duke in Northumbria, vassal to the king of England, with a session I was planning to eventually take maybe a county or two from pagan Scotland or something from my fellow English lords, while simultaneously maximizing the tech of Northumbria and the buildings within the county. I also wanted to befriend my liege lord just in case, and a few carousing parties with him and other fellow lords later he was my best buddy and when I requested a territory (after he had won a war with Scotland) he gave me the Hebrides. I was among the weakest in the realm, but still in a decent enough position.
Then the king of England died, and I was greatly surprised that the other lords had all voted that I should be the next king of England. Apparently the other guys liked me enough, since I soon after could make England primogeniture, i.e. my oldest child would inherit the throne and nobody interjected. I then conquered Scotland and made that also primogeniture.
My guy was getting old and he had four children: one older boy, two younger twins, one Content one Ambitious, and a genius fourth one. A good arrangement since Scotland allowed female heritage while England did not, so the older boy, i.e. me would get everything. Which was all fine and dandy until the older one died with only a daughter, aka the future queen of the Scots, not me. Then my guy died and I got to play as the Content twin.
At this point I figured that even though it's a sin and would risk me becoming a kinslayer, my niece the queen was just a wee baby and it would unite the realms anew, so I took a gamble and assassinated her, but alas I was found out. Soon afterwards my subjects revealed that it was my father's charisma that had made him king of England and they didn't care for me, since one of them had me excommunicated, and soon a faction with 240 % of my strength formed to make my brother the new king. I knelt publicly in front of the pope himself, begging him to lift my excommunication. It took me to a negative Prestige count but His Holiness accepted. It did not however stop the faction from firing, and a short war later I had lost the throne of England. Oh, and another subject had me excommunicated anew.
I was now only the king of Scotland and some territories in England when another faction to have me replaced with my child formed which had a higher strength than the forces I could muster, and they eventually succeeded, so I was now playing an infant with my genius uncle as my regent, an uncle that would become the king of Scotland should I die so I was really nervous that I would be assassinated, and I even encountered one time where someone tried to do that, it turned out to be him. Meanwhile in England my uncle the ambitious twin was having trouble keeping his subjects under wraps and he was eventually disposed by an older relative. And I could not pick my council based on who had the best stats; everybody hated me so it was only viable to keep the important people in the roles, and I had basically no army nor any income.
At this point the Vikings decided to raid through all my provinces and I was unable to do anything other than seeing how his army somehow grew while plundering my lands.
Then the duke of Jylland, Denmark, announced a prepared invasion for the throne of Scotland. He had twice as large army as I could muster.
"Of course he would." I thought, and went to bed since it was 3 a.m., thinking I should abandon this game completely. But I returned again, the day after, preparing for my inevitable loss.
But now the fortune turned. The Christian lords of Ireland all pledged their troops in defending my lands, and using the strategy of letting a lot of territory fall and thereby depleting the Danish forces of men, while also having invited the best commanders I could find to lead the armies and receiving a gift from the Pope since I was defending from heathens, I eventually managed to win that invasion. Then the king of England died childless and I got that throne as well. And could form the kingdom of Wales since the English lords had conquered enough lands.
This was a stable enough situation that I started planning for the future and educated all my children as Jews (I wanted to try how that would play out). I currently am playing as one of those Jewish children and honestly am surprised over how little my subjects seem to mind. There has only been one peasant revolt otherwise things have gone swimmingly.
That has been my run. And my takeaway from this would be: "Kinslaying: not even once".