i cannot shake this feeling

I spend my working week reading, studying, analysing, checking, re-checking, contemplating and then deciding what to buy/sell. I am not as thorough as i should be... but do seek wide range of info/opinion before investing. Yet despite my analysis....i cannot shake this feeling that 'overseas mkts are still fragile and another crash could happen almost without warning'. No matter how much i reckon a stock is 'safe'... this voice inside keeps nagging away. Does anyone else have this same apprehension?