When given a choice of dates, people choose their birthdates.
Its very simple. THere are 365 days in a year. So much choice. It is so difficult to come up with a random number off hand, and so the easiest is one which is etched in the memory of almost every educated human - his/her bday. That therefore becomes the number to choose, as well as the date.
Even our so-called random and sometimes consiously chosen choices are so often predecided on the basis of our history. Ranging from what we had no control over, but determines our lives to what probably happened.
No wonder it is so easy t prdit what most people will react to after stusying a given population set.
Our brain thus eventually is a computer which can only act as per data fed into it. the only difference with present computers being the range of data fed into the brain is much much more varied and immense compared to anytrhing man made as of now.
And to go against this natural flow would be too tiring to keep up. It is possible for a computer to perform on peak efficiency, but not 365/24/7.