Even the most committed athlete is going to miss training days. For reasons outside of his/her control, things such as sickness, family issues etc will always come up and its just something that has to be dealt with. Some would call these the "uncontrollables." However, what you can control is how you deal with these mentally and also how you adjust your training program.
Having one or two days off training is not the end of the world. In fact if you're body is incapable of getting through a session or is screaming out for a sleep in then it could quite possibly be the best thing to do, even if your program says otherwise. What we don't want to do is have too many days off and suffer the effects of detraining. You will lose your fitness twice as fast as you gain it and for those performance athletes this should be motivation enough to get your training done.
Alas, if you do miss training days, here is a easy reference table to guide you on the path back to training.