I've lived in the uk for nearly 6 decades, I've travelled to many countries in Europe and been to several cities during those years. I've seen guns on only two occasions. Once in Paris on armed gendarmes on the Champs Elysee and once on border guards in the old Yugoslavia.
Of course it's not to say it'll never happen, you just need to be vigilant in certain places. But if you put your life on hold just in case you might get caught up in something then you've let them win. It's like saying you're not going to go out in your car just in case you meet a drunk driver coming the other way. You have to be realistic and live your life to the full.