From Willy Bardos, 'On the Psychology of Piano Technique (trans. 1982),'...The normal course of playing is disturbed as soon as the regular succession of innervations is interrupted. This will happen if different innervations enter into conflict because of the pianist's lack of security, or because of fear of a difficulty still ahead....A premature impulse of the will generally occurs when a passage, or even just one of the hands, requires a stricter control, and consequently the pianist is quite anxious to recognize the difficulty soon enough. The exaggeration of this praiseworthy intention to react in good time will provoke disturbances in the innervation [the present innervation not the difficult one to come] or in the execution of the movement.'That was written in 1924!
