Nowadays there's a lot of people who are able to assassinate. Fortunately, it hasn't happened in Poland yet. That experience could change our lives a lot.
Fisrtly, I think people would became more careful and suspicious. They would notice more strange and uncommon things. Every stranded bag or bin could have colligation with terrorist attack.
One of the most important change is fear which can make our lives worse.
Checking on airports and stations could be more strict and compulsory. Department stores would employ more bodyguards.