Not sturdy, stop me topple, stand

With effort and me in your hand

You'll see, now neither fat nor slim,

Before was both, and that was grim.

But now what am I? Possibility. Don't scoff!

I'm on 'an off.

'So you're not sturdy?'
'I'm not sturdy. If anything, you have to stand me.'
'Are you an egg?'
'No.'

Riddle Answer Chance

Riddle Explanation
not sturdy, stop me topple, stand with effort and me in your hand - to stand a chance.

you'll see, now neither fat nor slim - a fat or slim chance, both mean of little likelihood.

but now what am I - what are the chances?

possibility. Don't scoff! I'm on 'an off - on an off chance.