you use a line of best fit for a set of data to make a prediction about an unknown value. the correlation coefficient for your data set is 0. how confident can you be that your predited value will be reasonably close to the actual value?
i can be very confident; it will be close, but it probably wont be exact.
i can be a little confident; it might be close, or it might be way off.
i can't be confident at all; this is about as close to a random guess as you can get.
i can be certain that my predicted value will match the actual value exactly.