I'm not sure if you feel the same way but it is always nice to get a little justification, particularly if you are an athlete. For me the best justification is that you made the right decision in regard to weather.....there is nothing worse than looking forward to your training session and then discovering as you exit the door (or look on the weather channel) that it is raining! For me I generally look at the local doppler every morning to see if I can get a ride/run in before any forecast bad weather.
This is where the justification comes in.....it can be very frustrating to see a massive green blob over Bowie on the doppler radar and decide that I have to head to the trainer in the garage or to the dreadmill at the gym. Now if I make that decision I want it to throw it down with rain for the whole day and so the loss of an outdoor workout is justified. If it rains for a brief period and the pavement is dry as I exit the garage or the gym and then it is dry for the rest of the day....now that puts a bummer on things! For that reason you need the justification!