Why human nature is so contradictory? Why we say "yes" today, and "no" tomorrow, so easily?

Answer 1

The accessibility to information makes it easier for us to redefine a situation. We need more time to really weigh of our options once we have all the facts we need.That's where the phase, "let's sleep on it and decide tomorrow" comes from. As we wait longer and more information becomes available we may change our minds.

Answer 2

That we say "yes" one day and "no" the other day does not necessarily indicate a contradictory nature. Circumstances change. Situations change. THIS is why you change your mind. You don't have to have a contradictory nature to change your mind.