You'd be surprised to find out what the source of negative energy is. You can place the blame on external factors but you would only be shirking taking responsibility for what is truly the source of the negative energy, which is YOU. You cannot control external events, but you can control your reaction to them.
What you focus on is what you give power. What you allow to affect you you give power.
The best psychic self-protection you can engage in is to use Will power, and to choose what type of energetic entity you wish to feed and which you wish to starve. Do you wish to live in a state of grief, or would you rather free yourself from it?
A quote which I think serves the subject nicely is, "You can't control the wind but you can adjust your sails."
I have said some things along similar lines on my current blog. The specific post of which I speak can be found here: http://visionsoftheworld.blogspot.com/2009/07/you-ask-about-negative-energy-heres.html