Infalibility is associated with the Almighty God, why is it not possible with human being?

normally I am infallible but in this case I am not sure

Because we are not almighty. It doesn't just have to do with imperfection, because Adam & Eve were perfect, yet they fell. However, the difference between us and them was that they chose to fall, we, because of inheriting imperfection after their disobedience, do not choose. No matter how hard we try, we will always make mistakes.

We are made in God's image, so infallibility is not impossible... anything is possible.

Origionally, people were until the first sin, sin and imperfection are passed down from each generation. We are born into it. It can be forgiven though.

whatever obi wan kenobi