How are samskaras (habits) formed in the mind ?

The mind is like a phonograph record .It contains grooves , or impressions called samskaras, in Sanskrit .These samskaras are formed when certain thought waves , or vrittis, become habitual .For example , a man passes a bakery and sees a chocolate eclair in the window .The vritti arises in the mind ," How delicious ; I will buy that eclair ." If he ignores that vritti , and turns his mind to something else, no pattern is formed .But if he identifies with the thought , he gives life to it ,he buys the eclair , looking forward to enjoying it as dessert that evening .Now ,suppose he finds he must pass that same bakery every Tuesday and Thursday .Each time he goes by , he recalls that wonderful eclair , and purchases another .What was originally just a flash in the mind has become a force in his life , and a samskara has been formed .

Swami Vishnu devananda from the book "Meditation & Mantras" pg .2

( Note : Here samskara = mental impressions , vritti = thought waves .These terms will be frequently used in Raja Yoga ) .