How daft are flying insects???

I have to ask this question because I have noticed recently that when I am sitting at home on a sunny day I suddenly hear the odd "ting" sound. When I look up I see a fly or wasp bouncing off the windows. Are they:

A) trying to wind me up by annoying my relaxation?
B) unable to register that the inside of a home looks different to the outdoors?
C) participating in an insect extreme sport - sort of the flying insects equivalent to bunjy jumping???

Answers on a postcard to the usual address!