I'm not so sure about that.

Meaning

I'm skeptical or uncertain about your statement.

Examples

• John: 'This will definitely increase our market share.'<br>
• Alice: '<b>I'm not so sure about that</b>; the competition is quite fierce.'
• John: '<b>I'm not so sure about that</b>; we haven't adequately addressed some crucial issues.'
• Alice: 'The new product launch will be incredibly successful.'<br>