This is the 217th most frequent Japanese word.
個
A counter for individual objects or items.
個 is used here as a counter for individual items, in this case, apples.
私は3個のりんごを持っています。
I have three apples.
個 here is used to describe parts or pieces in a collective sense, highlighting their difficulty.
このパズルは難しい個が多いです。
This puzzle has many difficult pieces.
個 is applied metaphorically to describe the individuality of small, distinct objects.