I recall Larry Williams writing about this in one of his books. Basically, he made the point that you can't be so worried about the money that it freezes you but neither should you lose sight of the fact that we are dealing with real money.
I think murray put it well. There is a cost of doing business aspect to losses. You have to accept that, but I would rather see someone too concerned about losing money than not concerned enough. Being not concerned enough leads to blowing out.
If the monetary risk is too stressful, I wouldn't say try to change your attitude. You probably will not succeed in changing it anyway. I would say understand why it is so stressful. Are you trading too big for your account? Are you trading with money that has already been dedicated to something important, like rent? I put it that way, because I don't like the usual way of putting it, ie "trading with money you can't afford to lose." To me, that sounds more like gambling.
You have to face the fact that not everyone is cut out to be a trader. Maybe it is the uncertainty that is the problem, the sense of randomness, and obsessing over money is simply a symptom.
The top hedge fund manager in the country, Steve Cohen, certainly obsesses over money. I read that if one of his traders has a 5% drawdown, he has half his stake taken away. A 10% drawdown will get you unceremoniously fired. He could give a crap if you were trading your plan, if you had 15 years of backtesting, if you had a zen-like focus, nerves of steel and iron discipline. Take a 10% drawdown and you will be working somewhere else.