Some pilots are naturally nervous Nellie's while others don't get fazed in the slightest. Forecast of thunderstorms and low vis at destination will really pray on the mind's of Nervous Nellies while same forecast would not unduly worry another pilot. Some of this might be traced to morbid reading of accident reports caused by heavy weather and of course all the grim flight safety articles in magazines. So the Nervous Nellie is primed for disaster from all quarters. You can reassure the NN's as much as you like but it doesn't help one bit. It's in their genes maybe. If they babble and shake when the radar shows a Cb in their path, best ignore them and certainly don't display your own doubts.