I was in Ljubljana last night and all comments that Poland have had a bad day or played on 70% are complete nonsenses
Poland played as much as Slovenia let them to play, Giuliani totally outclassed Heynen tactically and that's the reason for Polish loss. Anyone who says opposite is totally clueless about volleyball 
Slovenia played on 110%? Also a joke as several players, especially Urnaut looked pretty exhausted and tired but managed to find strength to pull out key balls and serves. Polish players looked much more fresh than Slovenians but that's not a surprise IMO. Slovenians played on 110% indeed but in several occasions
Let me return on tactics - THE ONLY chance for Slovenia to win this match was to risk on serve as much as thay can. Čebulj, Urnaut and Pajek were hitting jump serves in most cases, Kozamernik and Vinčić were taking big risks with his float serves as he was trying to hit the lines and they succeeded in their intentions. In same time they didn't take much risks in the attack, they made only 4 attacking errors in 4 sets against Poland and I think all should bow to them for that
Also they were focusing block on Polish wings as reception as quite poor and Dzyzga couldn't play with his middles much. Slovenia didn't have many kill blocks, their approach was to focus more on defensive block, leaving Kovačić and other players picking "dead" balls after the block. Vinčić isn't great setter, for me he is mediocre player with a lot of insecurity in his setting and that makes this result even bigger. If Slovenia have setter like or close to Kobzar/Toniutti level they would be much more dangerous team.
Poland wasn't bad at all, just remember Bienek and Kubiak serves in the end of 2nd and 3rd set, Leon killed several hard balls but to expect him to beat Slovenia alone is pure underestimation of Slovenia. Claiming 2-3 hours airplane trip had impact on performance is... better not to say anything. Simply Heynen missed tactics, didn't pull right moves and that costed them. Not playing on 70%. 
I also have to "reply" on comments Slovenia isn't world class team. Ok they aren't on Brazil, USA, France level but this team played final back in 2015, won World League Group 3 & 2 in just 2 years, beat Poland also in 2017 in Poland (!!) and for sure they can endanger even the biggest teams. IMO they would have more consistency if FIVB allowed them to join Nations League 2 years ago as they missed matches on high, international, level during that time and matches are the most important thing in becoming powerhouse. While Poland/Russia were playing with France, Brazil, USA, Serbia etc. Slovenia was fielding B/C squad in European League vs Finland, Ukraine etc. I'm not underestimating any of these teams but certainly they are weaker than Nations League teams.
Don't get comments which are underestimating Slovenian success but this is one nice story which proves volleyball is great sport.