I heard a golfer* describe preparing for a crucial put by saying “I couldn’t think anymore about it or I’d have wondered about every blade of grass, and that would have just been distracting.”
The same goes for mindfulness. It can be a complex topic if you so wish, but ultimately it must be simple. Know the body. Know the breath. Know the feelings. Know the mind and its objects.”
Or as I read a renowned Buddhist** describe it “Sit and know you are sitting and all of reality will be revealed to you.”
(* Martin Kaymer)
(** Anagarika Munindra)