That quote is just wrong.

It is possible both logically and mathematically.

For most systems/selection methods it will not work. I can agree with that statment but to put a blanket on it saying it won't work is incorrect.

If you have a high enough strike rate and the odds show a loss at level stake you can make a profit ising a progressive staking plan.

Mathematically it is always possible as there is no theoretical limit to how much you can bet.

Logically 99% of people stuff it up because they don't understand the risks and how to minimise them. For those that spend the time looking can make a nice profit. For the others who just say its not possible well that is too bad for them. If you play with it for a while you can see what the problems are ( ie large loss after x bets) and you can come up with solutions to them.

Good Luck.