Being a stupid consumer

In January I bought flight tickets from the Lufthansa website for a trip to Italy. At that point I did not know that I would change jobs and be responsible for a workshop on the day of my flight to Rome on the 4th of June. I called Lufthansa in order to try to get my ticket changed but as it was so cheap I could do nothing but cancel them and buy a new one and of course to a much higher price. I didn't know that when you buy a return ticket you have to be on the plane both ways otherwise the ticket is invalid. And the most important thing was of course that I would have to start the trip at the correct date. What I did was that I booked another trip for Rome with Air Baltic (which was a nice flight by the way) and thought that my Lufthansa ticket would have been valid from Rome to Helsinki on the 16th of June. I even checked it on checkmytrip.com the day before leaving Italy and it seemed that everything was okay. But nope. At the check-in counter I was told that my ticket was not valid anymore. I had paid 270 euros for a return ticket that did not exist just because I did not catch the flight on the 4th of June. So although I tried to negotiate it I had to buy a new one for 500 euros. Well, I got a 100 euro reduction because I bought a return ticket to Milan (as a matter of fact I could take the plane to Milan next Monday, lol). So in fact my trip that should have cost 270 euros cost 1030 euros (260 with Air Baltic + 270 + 500). The only answer for this was that it is a pricing policy. I am not a frequent flyer so I fall in the category of naive, stupid consumers that the big companies as Lufthansa can gain on. Onboard the plane I read Lufthansa's magazine and the words of the CEO. He was really satisfied with how well Lufthansa did on the market. One of the reasons was their way of handling cost-effectiveness. Yeah, right. And I think that happily enough they have stupid consumers, customers as me. Will I use Lufthansa in the future? I will try to avoid that if possible.