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

I do believe in this however in very rare cases there are some mummies with low supply. If you latch frequently and on demand, your body will make the necessary production to suit your baby's needs. When baby demands more he suckles more and the body produces more. It's part of mother nature. Some mummies worry about their supply and begin to supplement their feeds with formula milk and hence fall into the top up trap. I used to be one of them until I decided to take the leap of faith and have no standby formula at home.