Final answer:
Isostasy is the equilibrium of the Earth's crust floating on the mantle, akin to sitting on a couch where the cushions adjust to your weight. Atmospheric pressure doesn't prevent you from getting up because it's evenly distributed. Pressure on Mt. Everest is lower than at sea level due to less air above it.
Step-by-step explanation:
Isostasy is the concept in geology that Earth's crust is floating on the semi-fluid upper mantle (asthenosphere) similar to how an object floats on a liquid. The principle of isostasy can be compared to sitting on a couch or lying on a mattress. When you sit on a couch, the cushions compress and adapt to your weight, just as the Earth's crust sinks into the asthenosphere under the weight of a mountain. When you stand up, the cushions return to their original shape, similar to how the crust can rebound after the weight (such as an ice sheet) is removed.
Considering atmospheric pressure, even though it exerts a force of about 10 tons on the top of your body when lying on the beach, you can still get up because this pressure is evenly distributed across the surface of your body, and your internal pressure counteracts the external pressure. As for pressure differences, the pressure on Mt. Everest would be significantly lower than in your classroom due to the reduction in the amount of air above you at higher altitudes, demonstrating hydrostatic equilibrium where the pressure must support the weight of the atmosphere above it.