Why is having a sense of humour so important to those who practice magick? I see it recommended often.
I'm sure there are several reasons. For one, it serves to further distance the practice from traditional belief systems, which are typically super serious all the time guys. Also, the magical practice in question may be dependent on the worship of a deity/deities, many of which are considered tricksters, etc, and a sense of humor may help in interacting with them.
Additionally, if anyone finds out about your practice, they'll probably react with criticism or at least jokes, and humor can help deflect or deal with the situation.
Finally, from a social standards perspective, magic is weird. You'll feel silly when you start out, and it would be easier to laugh off the feeling and carry on than to try and force yourself to stay completely serious.
Well, think of Taoism."Do by not doing." "When the common man hears of the Way, he laughs." "Water is the softest of all things, yet it can wear down the mountain." It's how I like to think of things.
Because Our Goddess is the lady of magic.