I personally think excuses are the single most important factor to keep us from reaching our goals. It's easy to find an excuse for everything: Doing the dishes? Nah I do it later..
However, finding excuses to not get fit is probably the one thing people find the most variations for:
It's too hot, I am not feeling well and my favorite one: I can't do this because (insert reason).
Who doesn't feel overwhelmed or is fighting for time to plan out all the tasks you have to do during the day? Specially if you want to fit in an hour of working-out. A lot of people also take it as an excuse to NOT work-out.