What is the Overton window?
The Overton window is the range of ideas the public is willing to consider and accept — ideas a politician to could successfully campaign on. This window shifts over time, as it’s subject to the trends of social thought and norms. All social reform movements have to shift the Overton window to make progress. The concept of different races mingling in public, women voting, or animals having rights - on all these issues the Overton window has moved over time. Positions which were once viewed as unthinkably radical have become the prevailing wisdom, while those that were once considered mainstream are now outside the window, and unacceptable to advocate.
Examples of the Overton window
Say you want to advance the plight of animal welfare in our society, should you: i) make the case for a currently “unthinkable” ideas (like legal rights for insects)?; or ii) advocate for smaller, incremental changes (like more humane conditions for chickens on farms)? Namesake Joseph Overton contended that pushing for extreme positions is more effective. Though this remains an open and ultimately empirical question, that depends on the specific case being examined. In the animal welfare case, this is hotly debated (see, for example, the Wikipedia pages for abolitionism and welfarism). Another possibility is that the best strategy is a mix between two that creates an equilibrium: the stronger the radical pulling on the Overton, the greater the incentive for smaller, more incremental pulling.
This also applies for organisations at a smaller scale than nationally. Imagine you want to run a new project at your job. Should you push for your optimal project (taking a lot of money and time from competing projects), or for a smaller, more realistic, but sub-optimal one? It depends; see above.
Another policy change strategy is to pull the rope sideways. Instead of joining a side and pulling on the rope (of the Overton window), pull it sideways in a direction no one will resist. Instead of trying to push for increases or decreases in the overall tax rate (an area that gets a lot resistance from both sides), try to increase the effectiveness with which it is spent — something that is both more neglected (and therefore more valuable) but also easier to actually see changes in (because both parties would prefer to see it spent more effectively).