How quickly does a Social Worker become jaded? Is it preventable?

I was on the phone with a Social Worker from a mental health unit in a different area recently discussing a client who had a 15 year history of going through a vicious cycle of a dysfunctional relationship with his father, and his partner, roaming the streets, putting his Department of Housing tenancy at risk because of his alcohol abuse, ending up in hospital…
“Vicious cycles can be interrupted and virtuous cycles can be established.”
It was not more than a month ago that he had been admitted into the unit, so it was disappointing to see him back. I asked the Social Worker I had on the phone for his opinion on what went wrong this time. We talked about the vicious cycle and I asked, “What do you think might break the cycle?” He said, “I don’t think it’s possible… oh gosh, how jaded do I sound!”
We had a laugh about it, but it struck me later on that – yes, even in the short time I’ve been a Social Worker, I have found my deep pool of hope has become a little less deep and a little more shallow. I have discovered breaking the vicious cycles are not as easy as I’d wished. I seem to face more dead ends on the unending road of optimism.
How do you keep yourself from becoming jaded or cynical?