Use the tooltip for loyalty, hover your mouse cursor over it to see what is causing the plus and minus to his loyalty.
1. If you notice one of your governors or generals have loyalty in the red (0-2), and you don’t have enough money to do the “Secure Loyalty” action on the politics screen, it is strongly recommended you replace the governor or general, so their potential insurrection won’t be as dangerous. Without a province to govern, the insurrection won’t involve a region or province breaking out. Without an army, your rebelling nobleman will spawn a small army against you (usually four units).
2. Once you do have an insurrection, don’t worry… it will do wonders for you in the long run by smacking it down:
Once you defeat the insurrection army/armies, the rest of the noblemen in your court who didn’t rebel will gain a permanent +4 Loyalty bonus. To represent how they’ve gone through the fire with you and come out on the other side.
3. Check the stats on the nobleman’s wife. Some wives have a trait that gives minus to loyalty. It might be worth considering paying some gold to get them divorced.
4. If one of your noblemen has more influence than your king, this will give them a -1 loyalty penalty. You might want to attempt to diminish their popularity or increase your own.
5. Estates: The “Low Estates” tooltip means they think the king has too many estates and not enough estates distributed amongst the noblemen. It doesn’t necessarily mean that this particular nobleman wants more estates.
If you (the king) hover around 3-4 estates, these “Low Estates” should disappear for all your noblemen, regardless of whom you give an estate to.