A surprising decision

Today, I came across one more behavior of mind.
My friend asked me a question and i had two options to answer, i.e, first was yes and second was no, nut I was not sure which one to say. Next moment I found myself saying 'I dont know' and later on I realized that this was a more correct answer . Mind did not choose either of the options? b'coz I was not sure? or in the end it was so fast to decide that I even could not realize that the decision has been changed.

Was it because I was really trying to get a non-biased answer? what if by nature I was a dis-honest person who only wants to say the things which are socially favorable to him.