Stop and Take a Breath!

I've been to the carnival; I've been to the robber's den.

I've seen judges who are just and unjust.

Can't really judge them; I've been one to make mistakes, too.

I've also seen twins eating a delicious green fruit.

I've sat down in a comfortable rocker,

and eaten a steak pink in the middle.

What a busy fellow I am, yet I don't have a worry.

I've done and seen a lot, and all from a challenge,

But what have I never seen?

Thanks for reading this puzzle! As usual, please include with your answer an explanation for each line of the riddle. (Every line in this puzzle contributes something, by the way).

You are

AIR

Each line of the riddle is a description of

one or more words that rhyme with "air."

I've been to the carnival; I've been to the robber's den.

FAIR and LAIR

I've seen judges who are just and unjust.

FAIR (again) and UNFAIR

Can't really judge them; I've been one to make mistakes, too.

ERR (from @arbitrahj)

I've also seen twins eating a delicious green fruit.

PAIR and PEAR

I've sat down in a comfortable rocker,

CHAIR

and eaten a steak pink in the middle.

RARE

What a busy fellow I am, yet I don't have a worry.

CARE (you "don't have a care")

I've done and seen a lot, and all from a challenge,

DARE

But what have I never seen?

Perhaps this one is AIR again, since it is invisible to the human eye.

Title: Stop and Take a Breath!

People breathe in air in order to calm themselves down.

• Very nice! This is, of course, the correct solution. As far as the missing line, "make mistakes" is the synonym I had in mind. I think I'll let this question get a little more publicity before I give you the checkmark. – Brandon_J Apr 28 '19 at 0:11
• Ah, I see, I think @arbitrahj has the right answer to that one (sorry for answer sniping you btw!) – HTM Apr 28 '19 at 0:12
• Complete now. Great job! – Brandon_J Apr 28 '19 at 0:14
• Great answer, no worries on the snipe, I’m a fan of your puzzles! – arbitrahj Apr 28 '19 at 0:15
• @arbitrahj Thanks, and you're an excellent puzzle solver! :) – HTM Apr 28 '19 at 0:17

Partial answer to get things rolling...

I've been to the carnival; I've been to the robber's den.

Faire, Lair

I've seen judges who are just and unjust.

Fair, UnFair

Can't really judge them; I've been one to make mistakes, too.

??? , err

I've also seen twins eating a delicious green fruit.

Pair, pear

I've sat down in a comfortable rocker,

Chair

and eaten a steak pink in the middle.

Rare

What a busy fellow I am, yet I don't have a worry.

??? , care

I've done and seen a lot, and all from a challenge,

??? , dare

But what have I never seen?

Air??

• Very close; looks like you got sniped :( Good work, though! – Brandon_J Apr 28 '19 at 0:12
• Indeed, you have unfortunately been sniped. But fear not, for in two days hereafter, I will award your answer a bounty (probably of $100+$ rep to make up for a $\color{green}{\checkmark}$ given that this question is on a roll at the moment) :P – Mr Pie Apr 28 '19 at 21:46
• @MrPie I wish there were more people like you - and also, thanks for the extra publicity ;) – Brandon_J Apr 28 '19 at 21:51
• Wow. I didn’t know that was possible! – arbitrahj Apr 28 '19 at 22:19
• Sorry, I completely forgot about this.... and then for some reason, I remembered whilst I was procrastinating. A belated congratulations for an extra 100 rep! :D – Mr Pie Jun 29 '19 at 15:42