Travel mistakes

Today I read an article about some of the common travel mistakes that people make, Some of the things that they mention are over ambitious itineraries, over packing, travelling without insurance, arrivíng at the wrong airport and running out of money. I have have often made over ambitious itineraries. There are always so many things that I want to see and do and I tend to plan far too much. I used to start at 8 o'clock in the morning and continue all day, but next time I will try to avoid too many plans and try to find time to relax a little as well. I don't over pack, I am quit good at travelling light, but I once made another mistake. I was living in Italy and I studied psychology my own. I had to go back to Denmark to take my exam and I put all of my notes in my suitcase and checked it in. Bad idea! My suitcase didn't arrive and my notes were gone. Fortunately I passed my exam anyway, but I have definately learned to carry the important things in my hand luggage Which travel mistakes have you made? And how do you avoid that mistake in the future?