Imagine for a moment that there was some gentle seismic upheaval that took your house and tilted it 30 degrees without breaking anything. What was once a wall is now a crazy combination of wall and ceiling - and the ceiling has become a combination ceiling and wall. The floor is a hill that you have to walk up or down or across. You need a seatbelt to keep from rolling off the side of your bed, and mugs of coffee placed on the table slide towards one side and, if you're not careful, off the side (and possibly into your lap).
To keep it interesting, every once in a while that same seismic event happens again, switching the tilt from one direction to the other. And lastly, to add spite, there's a giant that is tilting your house along a different axis back and forth. Sometimes he's angry and he tilts it violently and sometimes he's tired and rocks it slowly, and sometimes he's asleep and there's almost no rocking at all.
That's life on a keelboat (the traditional single-hull sailboat that most people think of).
But life can be like that too. You think you have it figured out and everything's running straight and smooth. Then something happens and the world turns topsy-turvy. Those times can be benign and joyful such as the arrival of a baby in the family, or they can be painful. Either way, that ordered world, with nice straight walls and flat floor is suddenly askew.
If you've not prepared for it, things go crashing about, falling off the table and shelves and making the situation even more messy even while you're just trying to keep your balance.