It’s not a very good article, but please read it if you’d like.
Clumsy and immature people end up being really unskillful. You can't do your job if you're always dropping things and whining, can you? They're usually also really childish, if you didn't already guess that.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.