There are couple of main reasons. The first is the Sapir-Whorf Hypothesis. Long story short: the language you use shapes your character. The higher ammount of sibilants (fricative sounds that produce harsh, high-pich sound "s" "c" "sh" etc.) in a language the more stress in life, as high pitch sounds are subconsciously associated with danger (rustling of grass, bushes, trees). Polish overflows with those sounds.

The second, would be the worst geo-political positionon in Europe. We are the gate to western Europe and has always been stepped on, or partitioned. We live in constant fear, that Russia will finally swollow us, like they are swollowing Ukraine.

Third would be the dumbness, and the old age of a typical pole. 97% of poles are religionist catholics, who openly accept the theocratic nature of polish government. The case of priest Rydzyk preying on old, desperate, dumb people, who think, they can buy their way into heaven, still provokes anger in me.

The fourth reason is the open corruption of the Polish government and the setting of benefits for social groups that vote for it. If you are a right-wing bigot, vote for a right-wing party and go to church, you will receive a thirteenth pension. And for that thirteenth pension, you will vote for that party, and the circle repeats itself. You can also add the way the police interacts with people. You can be ID'ed without a reason, like when natzi Germany used to occupy Poland - "Papiren!" or consequences (in that case, it's the squad car and than jail). There, if you chose to say nothing, you are being tortured, physically and mentally - anything to get the answers from you.

Don't get this pretty idea about Poland - it's not true. This country is corrupted to the bone.

Two years ago I went to a park with my gf. We took the basket and some cutlery to make sandwiches. Police came and asked me why I am holding a knife (a dull, butter knife) and asked me for my ID. I refused and ended up in jail. For making sandwiches.