Theory of Poker Effective Odds Question

[htc1278]

I'm having problems seeing a practical application of the effective odds situation presented on pages 50-51 of Theory of Poker:

Let's look at an interesting, more complex application of effective odds. Suppose there is $250 in the pot, you have a back-door flush draw in hold 'em, and an opponent bets $10. With a back-door flush draw you need two in a row of a suit. To make things simple, we'll assume the chances of catching two consecutive of a particular suit are 1/5*1/5...

David then explains that the future rounds of required bet calling changes this from a good call to a bad call. I understand this but what I don't understand is how this situation would ever arise? Heads up in a $250 pot with only a back-door flush draw for outs and an opponent that is betting just $10? Could someone please provide a situation where this might happen? What was the pre-flop action? What are my cards? What is the flop? How does this happen?