Professional difficulties.
My credibility at work could be undermined if some idiot from a socio forum decided to start phoning people I know.
That's why I keep my secrets to myself.
I don't trust anyone completely, either here or irl. There are people (again, both here & irl) whom I like and respect and would like to trust, but imo there is no point in trusting someone if the trust isn't reciprocated, and as I'm aware that my general personality is rather dislikable and untrustworthy, I doubt anybody actually trusts me.
But then I don't really have much reason to trust, if your definition of trust is just not revealing secrets, as I'm pretty open these days.
I totally trust my RL friend but a trusting attitude doesn't mean you can rely on people. Those are different things. She would save my life if she could. She brought me beer and pizza yesterday. But also she totally forgets things, like promises to pick me up somewhere in the cold and dark, and I'm like Where the hell is she? So I also "trust" her to forget my needs and what she promised to do for me.