Shoulder season is recommended as the reliable way to travel cheaply. The saving is real for some parts of a trip and close to absent for others, and the split is predictable.
Accommodation drops first and furthest
A hotel has a fixed number of rooms and a strong incentive to fill them, since an unsold room earns nothing while costing almost as much as a sold one.
As demand falls, rates follow quickly, and properties that were unavailable during peak weeks become both available and discounted within a short period.
This is why the largest shoulder-season savings appear in accommodation, particularly at the upper end where peak pricing had the most room to fall from.
Airlines cut capacity instead of price
An airline can move an aircraft to another route or reduce frequency, which a hotel cannot do with a building. Supply shrinks alongside demand rather than after it.
Because seats are removed as passengers disappear, the remaining flights stay reasonably full and fares do not fall nearly as far as accommodation rates do.
On seasonal leisure routes the effect is stronger still, since the route may stop operating altogether, leaving connecting itineraries at higher fares as the only option.
The weather is the reason demand fell
Shoulder pricing exists because conditions are less reliable, and that is a genuine trade rather than an inefficiency waiting to be exploited by a clever traveller.
The risk is not usually bad weather throughout but variability, with some excellent days and some that rule out the activity the trip was built around.
Trips with several possible uses for a day handle this well, and trips that depend on one specific condition handle it badly.
Opening hours contract before prices do
Seasonal restaurants, boat services, mountain lifts and small museums close early in the shoulder period, sometimes before the accommodation discounts have begun.
The result is a window where prices remain high and services are already reduced, which is the worst combination and is worth identifying before any booking is made.
Checking the opening dates of two or three specific things you intend to do is a faster test of a given week than any general seasonal advice.
The best weeks are narrow and identifiable
The genuinely good shoulder weeks sit immediately after peak demand collapses and before services close, and that overlap can be as short as a fortnight.
It differs by destination and by activity, so the useful question is when the local season ends rather than when the school holidays happen to finish.
Travellers who identify that window for a specific place, and return to it, get most of the peak experience at a substantial discount with the trade-off understood.