[ElliotH]

Easily discernible for me. Its an awful lot like your tennis analogy though.

"I could take on anything my opponent would throw at me and without even breaking a sweat"

If I'm 'in the zone' as it were, you could replace 'opponent' with 'bugs' and it would be very similar to my experience. Not so sure about 'expending very little effort' though. While it doesn't feel like hard work while I'm coding 'in the zone' I end up completely mentally exhausted by the end.