there are more factors than that, though
you're looking at it from a point where there are only 2 characteristics
The principle applies even better with more factors. If you pick 3 out of 10 and ask them their favorite color, and two say green and one says red, you can't assume that 2/3 of the population likes green and 1/3 likes red. However, if you pick 333,333 out of 1,000,000 and ask them their favorite color, you can get an accurate representation of what colors that group of people like.