The possibility of a pass failing to meet its destination. Xavi often had that in mind but managed such numbers of through balls and chances created due to exquisite creativity. Basically, that's Xavi pushing the brake pedal, his cost benefit analysis.
Through ball is a pass splitting the defence for a team-mate to run on to. The highest quality/hardest of a pass you can expect from a passer. Xavi was so good that Bobo32 think it is normal pass and Xavi played no risk or less creative than Puig or Arthur.