"I don't know" , it's a short sentence, but many people are ashamed sometimes to say it!
In Islamic religion, it's unlawful to give an Islamic legal opinion (fatwa) without knowledge; so if one was asked about a certain judgment, and he didn't knew it, he only needs to say: "I don't know"
The prophet peace be upon him, he said when he was asked about a certian thing, he said: "I don't know, I'll ask Jibril".
This shows that saying " I don't know" when you really don't is not something to be ashamed of, the prophet himself said it...
It's an enormous sin to give an Islamic legal opinion without knowledge, However, many people these days commit this sin, and some of them are claiming to be "sheikhs", and when they're asked, they don't say I don't know to let people think that they have the answers for their question, so they talk without knowledge, and the one who does this Allah damns him because he commited an enormous sin.
And sometimes, by talking without knowlege, a person may even blaspheme, we seek refuge with Allah ta^ala from doing that.
Allah knows best.
