It is exceedingly difficult to do the shading with pencils

Yesterday when I posted my first sketch of geese done with B, 2B, 3B, 4B, 5B, 6B, 7B and 8B Faber Castell pencils, Hive account@lildebbiecakes suggested I could try to draw a circle, a triangle, a rectangle and a square and apply different shadings with these pencils.

I tried it and found out it's so difficult to do properly.

So I need to practice doing it over and over and over again.

By the way, here is how smoothly Hive account@lildebbiecakes did it: