You've arrived at the airport two hours before flight, 'cos that's what the travel agent said. Then you whizz through the check-in and security clearance and have nearly two hours to kill on an uncomfortable seat in the departure lounge! The two hours is built in for many reasons. Firstly, there are a lot of flights each day from the airport, which means lots of passengers and baggage to process.  I hate rushing, so arriving at an airport with minutes to spare and finding myself in a long queue would stress me out completely. Therefore I go early, and mellow out. Secondly, there are the security aspects.