The mind is supposed to be the fastest known thing, though less understood. Ishavasya Upanishad talks of Atman as being faster than the mind so:
अनेजदेकं मनसो जवीयो नैनद्देवा आप्नुवन्पूर्वमर्षत् ।
तद्धावतोऽन्यानत्येति तिष्ठत्तस्मिन्नपो मातरिश्वा दधाति॥ ईशोपनिषत् ४ ॥
Unmoving, It is one, faster than the mind. The senses cannot reach It, for It proceeds ahead. Remaining static It overtakes others that run. On account of Its presence, Matarsiva (the wind) conducts the activities of beings. (Translation by Vidyavachaspati V. Panoli)
In Bhimarupi Maruti stotram, Samartha Ramadas Swami says:
आणिला मागुती नेला आला गेला मनोगती ।
मनासि टाकिले मागे गतीसी तुळणा नसे ॥
He brought it in and took it back, both with speed like mind; verily he surpassed the speed of mind, his speed has no comparison. (Translation by sanskritdocuments.org)
The former shruti quotation shows that mind is the fastest known and Atman is the (only) one faster than that, while the latter stotra reference is a praise to Hanuman as being faster than the mind, meaning that Hanuman is Atman itself.
Now that we've established that short of Atman, mind is the fastest, lets see what this essentially means. In avasthAtrayA parIkshA, having understood that the Self is different from the various koshAs, most one can achieve is paroksha j~nAnA. For aparokshA j~nAnA to arise, there has to anubhUti of the Atman. However, while moving from one avasthA to another, most importantly from dream or deep sleep to waking state, the naisargika or natural tendency of the jIva is to get bound to dehAtma buddhi. All of us have experienced, at one time or another, that immediately upon waking up from deepest of sleeps, there exists a few moments of a lost feeling, a feeling where we know not where we are, what we are doing, etc. Then slowly it dawns upon us as to we are in such and such a place and thats it, all memory is regained in that instant, without needing further delving as to what exactly happened to us! Then goes on an outward planning of our day or what have you. However, those few moments, or truly fractions of a moment, is of utmost importance. Thats a sandhi. Thats when anything can happen; it holds immense potential to understand the infinite!!
Lets step back a bit. So what exactly happened when that memory flooded back on gathering back the geographical presence of ours? What we lost there is that even before "where am I?" existed a question as to "who am I?" That question slipped our dullard minds, habitually. We have, across janmAs, trained ourselves to forget the important question itself, let alone wanting to find the answer. What we realize, therefore, is that we couldn't place ourselves as to where we were and thankfully we regained it soon after. If we were to know that the we identified ourselves as this body and then the mind found that this body is placed somewhere geographically in the vast created space, we would know that there was some state prior to this binding, which is our sahaja stithi, true nature, au naturel! That tremendous potential exists right there! Simple!
Alas, that simplicity is extremely difficult to come by. I mentioned the ill training across countless lives. But herein, ties in the speed aspect of the mind. That binding is so fast, that of false identification of me and mine, that there is no tool available at our disposal which is faster than the mind to stall this process, or even slow it down. Here, Vedanta comes to the rescue, using tools as described in Sankhya philosophy. Sankhya says that the antahkaraNa manas itself is divided into manas, buddhi, ahaMkAra & chitta. The binding, quite a series of binding events, that happens is that of the ahaMkAra with the body, assisted by the thinking manas, chitta bringing forth the memories all at once and we get lost in this prapa~nca. Interestingly, that the buddhi or the intellectual aspect of the mind is still asleep and late to wake up is not an accident. Its created so and aged lazy by habit so as to keep the creation ticking! The sleeping intellect is what causes an almost insultingly dull feeling, so to say, since we have moved to analyze our sharpness with our alertness to this outward world. The fact is contrary to this. We ought to train ourselves back to reality. The trick lies in waking the intellect up earlier in the cycle so much so that the binding hasn't yet happened and never does happen! All our sAdhanA is really focused towards this singular goal, a complete end in itself, that of sharpening the intellect and training it against this binding taking place after which it has no control. Another way, sAdhanA can be understood as slowing down the pace of the mind from binding. The binding can be likened to an arrow being shot in the outward direction towards the world when the mind is out there to the point of no return, let alone changing direction in the opposite direction. The intellect waking up early can stop this outward arrow being shot, which means that the jIva remains in its essential state as the Atman.