A: Where do you stand on the nature-nurture controversy?
B: Me? I guess I think family is the most important factor. A happy early childhoold makes a person cheerful for life.
I heard an American say this in an interview. Why did she say 'I guess I think'? She could've said either by why both? I don't understand the meaning.
"I think" could mean that she had thought about the question, and this was her considered opinion, or that she was only now considering it (it would usually be obvious from how she said it which of these was the case).
"I guess I think" strongly suggests that she was only now getting her thoughts in order. In fact, I would argue that the "I guess" was mostly a filler, to give her time to think of the answer.
You have to be careful about reading too much into grammar during verbal interviews. People often say things they probably wouldn’t write if they had a chance to proofread their text and polish their prose.
You are right, the speaker could have used either phrase and probably doesn’t need both. I would guess that the phrase was uttered without much thought, as her mind was probably more focused on her answer to the question.
That said, the phrase is not ungrammatical. Lead-ins like “I guess” or “I suppose” often indicate someone is giving their initial impression about something they may have not ever given much thought to previously. Had the speaker said:
I think family is the most important factor.
That sounds like a strong opinion with not much room for wavering. The speaker may have also said:
I guess family is the most important factor.
but that sounds like the speaker is unsure. By saying:
I guess I think family is the most important factor.
the speaker is giving an opinion, but not being dogmatic about it.
I guess I’d say that the language sounds acceptably idiomatic to me.
It indicates the undecidedness in the mind of the candidate. It is possible that she doesn't have a clear opinion on the controversy, however feels that if she has to choose, she will go with the aforementioned opinion.
