Marx and Engels advocate this idea that capitalism is a runaway train, destined to sow the seeds of its own inevitable destruction. Their premise asserts that there is no limit to capitalism, as the desire for individual profit knows no ends. A wealthy industrialist who owns ten factories will seek to open ten more in the hopes of maximizing their own margin of profit. This will give way to more factories as the cycle continues. While the other members of the bourgeoisie will do the same. As these individuals will generate more money, they will also generate greater hardship on their workers. For each factory owner who makes incredible profit, there many more workers who are denied basic subsistence, poor wages, and exposure to inhumane conditions of work. At some point, Marx and Engels argue that these narratives will increase until it will become evident that the needs of the many will overwhelm the material desires of the few. This is a fairly democratic principle: The anger and perceived unfairness from the workers' point of view will percolate to the surface and cause the change in the ownership of the means of production. Eventually, with each increase in the success of the bourgeoisie, the anger of the workers will increase and the inevitable power shift moves closer to becoming a reality. This would be why the bourgeoisie is producing "its own grave diggers" above all else.
As per Marxist concepts, bourgeoisie is the class of people who own and manage the means of production. At the dawn of industrial revolution the bourgeoisie was the downtrodden class with the feudal occupying the position of dominant class. But over a period the bourgeoisie as a consequence of industrial revolution overthrew the feudal power to become the dominant class. In this way bourgeoisie acted as, as per Marxist terminology, gravediggers for feudal.
Karl Marx as well as subsequent prominent communist leaders like Lenin used the term Grave digger to describe a rising revolutionary class which is destined to overthrow the ruling class. Marx wrote that though bourgeoisie acted as grave diggers for feudal, now by creating a vast under privileged working class their own grave diggers, as this oppressed class is bound to organize themselves and overthrow them in a revolutionary way.