Inexpertness

used to describe a person who seems to be incapable of doing something due to a lack of necessary resources or skills

It may be too difficult for the trainee - small dog, tall weeds!

used to say that someone is extremely bad at doing something

He can't paint for toffee!

a person or thing that excels at doing only one thing

He's a one-trick pony when it comes to cooking, but his spaghetti is legendary.

used to say that one did not have much experience with something and therefore is not very good at it

I used to be a great piano player, but I'm out of practice now.

having little knowledge or experience of a particular situation or activity

He's a talented musician, but he's still wet behind the ears when it comes to performing on stage.

to lack knowledge or understanding of a particular concept or term

When it comes to modern technology, my grandparents don't know the meaning of the word.

an unscientific or inaccurate estimate or method

He didn't have any data to back up his claim; it was just a finger in the air.

a person who is competent in many different tasks

John is a real jack of all trades; he can fix the plumbing, repair the roof, and even bake delicious cakes.