Work that is too easy is boring. Work that is too hard produces failure and quitting. Motivation is highest in the narrow band between the two.
Plot motivation against difficulty and you get a curve. At the low end, boredom — too little difficulty, nothing to engage with. At the high end, failure — too much, and the effort stops feeling worth it.
The peak sits in the middle, at what Clear calls just manageable difficulty: hard enough to demand attention, achievable enough to be worth attempting.
Delegation. A task that is trivially easy for someone teaches nothing and bores them; one far beyond them produces a mess and damages their confidence. The right stretch is slightly beyond current ability with support available.
Targets. A target the team knows is unreachable produces the same disengagement as one they will hit by lunchtime.
It is the same shape as the [performance zone] — comfort, stretch, danger — drawn as a curve rather than as rings.
Ties to motivation theory — useful alongside Herzberg on the work itself as a motivator.