Most good PR people are paranoid. Admit it. You are. This is because it pays to think through what might go wrong. For instance, how might this story be interpreted? What potential crises are looming? What happens if the laptop fails in the presentation? What if there's traffic on the press tour?
The mantra is plan for the worst and hope for the best. It's a recipe for long hours and sleepless nights. Get used to it or get out quick.
Personally, I'm fine with scenario planning and asking the awkward questions you're not supposed to ask. But there comes a point where healthy paranoia becomes, well unhealthy. There are plenty of things to worry about in PR. We're paid to do that so clients don't have to - it's called responsibility. But there is a point at which it becomes destructive and you end up chasing phantoms.
Getting the right level of paranoia is hard. Too much and you end up burning cycles and midnight oil on increasingly unlikely events. The trouble is - it's a vicious circle. The one time things go off course becomes a justification for a mountain of purposeless planning.
Paranoia yields decreasing marginal returns. Knowing when to stop can make the difference between a sustainable work rate (and mental state) and burn out. In general, the management of paranoia is a function of experience. Newbies tend to lack sufficient paranoia until they make a mistake and pay the consequences - you don't do it twice. Veterans have seen the cycle a few times and know enough to handle issues if they crop up. I find the crunch point is in between - the account management level - when you know the consequences but lack the flight time to put the risks in perspective. Here be demons.
Sad to say though, the demons are personal. No-one can make you not worry, however much rationalizing they may do. And, heck I'll recruit people who care enough about these details every day over the blase Devil may care types. But recognize the trait and learn to harness and manage it. Healthy paranoia is a good thing, but it has to be just that, healthy.