I read that a mother will always be able to produce enough breastmilk for her baby? So is low supply just a myth?

Many times, mothers think they have low milk supply when actually there are a lot of factors affecting milk supply. Frequent on-demand latching or frequent pumping ensures that the breasts are emptied so the breasts can produce milk. A poor latch or supplementing with formula may cause milk supply to decrease. http://kellymom.com/bf/got-milk/supply-worries/low-supply/