I agree both parties time is valuable and should be respected. I know I'v had times when I'v had to cancel or ask for a bit of extra time. As with 99% of the gents here I have a regular job and it does get in the way sometimes but I try my very best to let you know as soon as I know.
In my real life job theirs a million things that can happen.
#1 is children most of us have them I happen to have a few more than others and two have disabilities.
#2 real work I'm in the medical field my patients have already paid me to care for them (they always come first)
#3 traffic and or getting lost. I'm the worst with directions even with a GPS I can get lost in a paper bag.
Even if these things do happen a kind phone call, text or email are in order by which ever person having the issue.