Using those Positive, Neutral, and Negative stability terms from PuffinBlue's comment, is the problem that we want positive stability, but the MAX without MCAS exhibits negative stability at a certain part of its flight envelope?
That is, if the pilot is holding the airplane with a constant amount of force and the airplane is climbing at a certain angle, some turbulence or other disturbance could cause the nose to pitch up, and then continue pitching up?
That is, if the pilot is holding the airplane with a constant amount of force and the airplane is climbing at a certain angle, some turbulence or other disturbance could cause the nose to pitch up, and then continue pitching up?