I fast on Tish'a B'av, but not on Yom Kippur. For several reasons:
- This is the real reason -- the rest is just a rant: Because i'm home with my 100% secular parents and with motivation to surf the web, listen to some music and study some DBA'ing and without Hadar, her parents or any religious or non-religious friends to motivate me to fast. With my parents i am kinda less Jewish. It is a horrible description, but i can't think of anything better.
- Because Tish'a B'av has more historical significance, while Yom Kippur is "just" a commandment. So the secularist-nationalist satan inside me says that Tish'a B'av is important, and commandments are really just traditional superstitions. But, as stated above, this terrible blasphemy is nothing but a rant.
Hadar is home with her parents, fasting and not using electricity, fire or musical instruments. Pretty strict. It is quite likely that if i spent Yom Kippur with her (with or without her parents!) i would fast, even though she would probably not want to. Strange world ...