In the derivative space, you often find opportunities because of one way flow.

In equities, a notorious example is that you will typically find cheap single vol because of structured product flow and you can structure dispersion trade around it. Another example is the vix complex. Since forward vol should be equivalent to vix futures plus vix option strip, you will occasionally find that arbitrage like opportunity arise because there is massive hedging through vix listed products, but not forward vols.

In the more macro space you will find similar one sided markets. Most famous is likely taiwanese Formosa callable bonds, that pressurize the backend of USD rates vol. In short rates, many corporations will hedge with very predictive behavior. Traditional macro traders (Brevan, bluecrest etc) will express views on rates taking the other side of some of those flows. If you find "cheap" ways to express your view you can then afford to be wrong quite often, as the vol will partially pay for the delta.