What political realities effectively limited absolute monarchs?
The major limit on absolute monarchy was the fact that there were many other people or entities that traditionally held at least some degree of political power. It was very hard to actually take power from those people. Two examples of these rivals for power were the nobility and the Church. Both had many rights and powers that they had traditionally enjoyed and which they were very reluctant to give up. The nobles had military power to back up their claims as well as financial power. The Church had financial power and spiritual authority in an age when religion was taken more seriously than it often is today. These sorts of realities limited the power that "absolute" monarchs could actually wield.