I'm not sure about it.
'Ne' — short, unstressed. 'Sicuro/a' — si-CU-ro. Stress on the second syllable. Gender: sicuro (m) / sicura (f).
Use to express uncertainty about an opinion or fact — you haven't formed a view yet, or your view is tentative. Prevents you from stating things as facts when you're not certain.
'Ne sono sicuro/a' means 'I'm sure about it' — 'ne' refers back to the topic at hand. 'Non ne sono sicuro/a' negates this. The 'ne' pronoun is essential — omitting it would sound unnatural ('non sono sicuro' is possible but implies uncertainty in general, not about a specific thing).
Ho i miei dubbi.
I have my doubts.
More expressive — implies not just uncertainty but active scepticism
Non mi è chiaro.
It's not clear to me.
'Non mi è chiaro' — the thing hasn't been made clear — could blame the explanation
Ci devo pensare su.
I need to think about it.
'Pensarci su' (to think about it) — indicates you'll form an opinion later
Expressing uncertainty in Italy can be perceived as a lack of conviction. Italians often prefer decisive opinions. However, in intellectual and professional contexts, admitting uncertainty while explaining your reasoning is respected as analytical thinking.