You double your bet every time you loose.

What people don't realize, is that doubling your bets is equivalent to an exponential increase. Here's a pic to help you grasp the exponential feeling:

http://www.regentsprep.org/Regents/math/ALGEBRA/AE7/fixpic2.gif
( I don't own copyrights on this image )

It's not sustainable. You run out of cash very quickly.

Additionally, if you are into statistics, you can calculate the expectation of this strategy:

https://en.wikipedia.org/wiki/Expected_value

The expectation value will be below 0.5, so the house will still have the advantage.

By the way, you will never find a casino game where the expectation value is over 0.5. The house would be loosing money over time in such a case.

Cheers!