What's the single most important requirement to learn something new?

To me: They are persistence, discipline, and organization.

Having an open mind would top the list, in my opinion.

They themselves have to want to learn and then have the motivation to learn.
Hard to single out 1 as I think a combination of requirements would be better.

I would say the passion.  Without it, one would find it is rather difficult to muster the necessary motivation, then dedication in learning.

I have passion, I have goals and I myself always want to learn new things but without discipline and concentration, nothing succeeds.

I would think that answer is dependent on which stage of life you are in. At every stage, the factor could differ. Is it for survival, for work purpose (then, you better be internally motivated, somehow and find the concentration somewhat).  Or, are you learning for interest, at a leisurely pace (then, only passion comes in).