What is concentration? Is to have your attention totally directed to one thought. The goal of meditation is to have no thoughts, which is totally different from mindfulness, which is just attention on everything you do.

Samadhi or illumination is attained without thoughts, mostly with a help of a 'koan' like: 'we know that all things can be reduced to unity. What unity is reduced to?'

Then the mind cannot answer and will start to evade and even give illogical answers, then the mind, when tired, stops looking for answers and go quiet, and that's the goal of meditation.