Unless you were lucky enough to take the Concorde before it was grounded, you rightfully equate international travel with flights of six hours or longer. Much longer in some cases – some regularly scheduled flights approach 20 hours in length.
Although the psychological burden of taking such long flights diminishes the more often you fly, the fact remains that unless you always travel in first or business class, you will likely encounter discomfort on such flights. This is compounded by the fact that the age and quality of planes, as well as the number (and size) of people around you, change from flight to flight.
For these and other reasons, you shouldn’t go into a long-haul fight expecting it to be pleasant, no matter how adept at intercontinental flying you are. Developing best practices, however, will help you more swiftly and effectively deal with discomfort and annoyance as they arise.