I think, by nature our mind is always open. It is like a sponge, gathers and remembers all the information it encounters. Sadly, most of it goes to the subconscious level. On the conscious level we make choices, we pick what we like and discard what we don't. Do we really? As I said, the mind gathers everything, even the things we don't like, accept or agree with. They all stay as seeds/data in our subconscious and when the right time comes, suddenly (sometimes years later) we change our mind about things and matters. Something we did not accept in the past becomes normal at the present time. Such changes may be sudden or as a conscious process when we gradually see, accept and understand that the person, event, thing, matter etc. we did not agree with was good, true, right or valid.

Commonly, having an open mind means willing to listen and acknowledging what is heard. We don't have to agree with what we hear.

Cultivating openness of the mind requires patience, tolerance and many other qualities. I think it is not really easy to do that on the conscious level. We show open mind toward people we agree with but easily loose our patience and close our mind when we face a person who presents views we don't accept.