There are many on line resources to describe the problems of micro stepping a stepper motor.
The following link
https://www.zaber.com/microstepping-tutorial
describes micro stepping in terms of motor coil current phaser.
( a phaser is a vectorial representation of current or voltage as a complex rotating vector )
A stepper motor can step from stable pole position to stable pole position when coils are digitally driven either high or low ( in a particular sequence,
Micro stepping is driving coil in an analog fashion( modulating phase and magnitude of the coil current).
Stepping a stepper can be achieved through the use of simple switching schema whereas micro stepping is quite a deal more complex and requires a specialised driver in order to provide the required current phase and and magnitude.