Who says that pressure is that important?
Sure, observing every single detail and football shows that last for hours where even a badly taken throw in is discussed, will force you to pay more attention to such details and become a better ref, but there is also another thing here, and that's how the game is played. You can't compare the football played in the top leagues with the football played in the Croatian league or the Finnish league. The football is faster, players run more, things are happening faster, you have to run more and be everywhere, see everything. Players in the Croatian league run some 2,3,4 km on average less than their Italian or English counterparts. That makes the officiating easier in Croatia.