It is easy to say but hard to implement. I have tried to control my betting size as well as time of the session. But with time and at some point everything fails.
Everything fails only because you are not determined enough to control it and do what you set from the beginning. You are the main reason that it all failed. If you are determined enough to stick to the plan than that wont happen. Even if it does happen then the chances for it to ruin yourself should be low enough