NightWolf_2112 on the official forums asks the question:
I am just curious to see how many crafters out there really live on the edge or are you not that adventurous and will be sure (100%) they will succeed!
I am not very risk adverse and most of the time use the maximum number of improvement items to guarantee a 100% success rate. The times I don’t are those late night crafting sessions triggered by a request just as I am about to logoff.