When one considers the surface area of a door or window exit multiplied by the air pressure pushing against it, you'd need to be able to move several thousand pounds in order to force open a door or window.

Cabin air pressure at cruising altitude is lower than air pressure at sea level. At a typical cruising altitude of 11 000 metres (37 000 feet), air pressure in the cabin is equivalent to that at an altitude of 1500–2500 metres (5000–8000 feet) above sea level. Which explains why my ears don't pop nearly as much flying in and out of the mile high city of Denver!

Let's say a window exit measures 3 feet by 5 feet. Sea level air pressure is 14.7 pounds per square inch. (Cabin air pressure would be less, but we'll use 14.7 psi for this exercise). Hence the weight of the air pushing against that window exit would be nearly 32,000 pounds or 16 tons (2160 square inches of exit multiplied by 14.7 pounds per square inch).