Why do people break in your house and steal the stuff you worked soo hard for?

I work my *** off to get the few nice things I have... I dont live in the ghetto or a high cl neighborhood... Im jus a hard working man who got out of the Army a few yrs ago... lost everything in a divorce... got the strength to get back on my feet... bustin my *** to get my tools for work and keep my job.. then someone robs my freakin house.. W T F.... side question... can you kill someone if they break into your home in California?