Low First Step
A low first step on a set of stairs can be dangerous, for anyone
walking up or down a stairway. We tend to get in a rhythm, while taking
each step and something like this would probably be worse if we were
walking down the stairs.
Low first steps can be created by inexperience stair builders, but the most common stair building problem like this, seems to happen during a remodel or when someone adds additional materials to the bottom of a stairway.
I've seen stairways with additional concrete poured around the bottom for a variety of different reasons and remodels where a walkway has been removed, in order to raise it, for the sole purpose of creating more walkway or patio slope for water drainage, leaving the stairway with a low first step.
In other words they solve one problem by creating another one.
Here's a side view of a stairway that is been built correctly, with equal risers.
Here's the same stairway with additional materials added to the base
without understanding how it will create a low first step.
Remember, it won't be a problem as long as you add the same sized materials (thickness) to the lower and upper floors and each step of the stairway.