Back in the middle ages, there was a travelling show which travelled throughout Europe. It was famous across the whole continent for it's fabulous and death-defying shows.

The show was named "The Show of Tension", because of the daring nature of most of the stunts, and thus the performers and other staff associated with the show gained the nickname "Tensions".

Sadly, the shows didn't survive the poverty that swept Europe in the middle ages. As people got poorer, they couldn't afford to spend money on frivolous things like a travelling show.

And thus was born the expression "unable to pay a tension"...