Re: monopoly is when one firm has control of an entire market.
"But that very act creates the normalizing forces that will destroy them unless they have government protection. Since they have an economic profit, it behooves another firm to move into their market and undercut their price. The only problem(s) is/are potential barriers to entry in the market. Usual barriers are the amount of capital or labor needed or government regulation; of the three only government regulation is nearly impossible to overcome unless you are the incumbent."
Explain natural or "de facto" monopolies, then. They can occur because the barrier of entry is inherently high. For example, utilities industries that require lots of eyesore infrastructure to operate, like an electric or sewage company. If a rival firm wanted to butt in, they'd have to install THEIR OWN infrastructure alongside theirs, creating a NIMBY situation that's pushed by the people, not the government. Here, the incentive to create competition is countered by the NIMBY disincentive.
Similarly, some resources (like spectrum) are physically limited (there's only so much spectrum to go around, they have fundamental limitations, and the maximum amount of raw data they can carry is fixed according to mathematical calculations) and have no practical alternatives (Know anything else nonphysical and undetectable to human senses that can work through solid walls over long distances?). These would need to be regulated or someone will eventually gain control of all of it. Here, the resource is practically irreplaceable, precluding any kind of disruptive force.
Lastly, even if neither scenario was in place, a monopoly could obtain enough power over the market to be able to weather a disruption or even coerce the acquisition of said disruption. That's why I use the poker example. Even in a "rebuy" tournament (where one can buy back into the game), you're still at a disadvantage against a chip leader with a huge chip count advantage over you. Even with several rebuys, the chip leader can still bully you around AND withstand a few all-in losses from you only to take it all back by winning one himself. IOW, the disruption would have to be an absolute game-changer or the monopoly still has a chance to withstand or absorb the competition.