CK2's random events are supported by code that makes sure that certain things are true before they appear, but the cards in the board game are still played regardless of whether or not the event can be resolved. It's how I ended up with my rotten sons so quickly. Too many cards make you have another kid, despite players being limited to only three. Unfortunately, it's equally possible to go a whole turn without a single event doing anything because none of the players meet the requirements. It's a bit counter-intuitive, but when there's disease and unrest and spouses dying, it's a pretty convincing illusion of dynamism. Sometimes they'll harm you or help your opponent, allowing you to become the architect of your own destruction. The events are always completely disconnected to the actions and capture some of CK2's randomness, but they can be played tactically and weaponised, too. A tax card could have an event where the next player has a new baby, while an assassination card might also summon a plague.
