It's all in your head: 1668

First then to speak of Feavers or Agues; the House-wife shall know those kinds thereof, which are most familiar and ordinary as the Quotidian or daily Ague, the Tertian or every other days ague, the Quartan or every third days ague, the Pestilent, which keepeth no order in his fits, but is more dangerous and mortal: And lastly, the accidentall Feaver, which proceedeth from the receit or some wound, or other painful Perturbation of the spirits.

--From The English House-wife--

Like the fever that comes every three days, sometimes the patterns we impose on the things we experience keep us from seeing what our real problems are. All we get out of it is an explanation; and for some people that's good enough.