B.J. FoggPhD · behavior scientist, Stanford University (Behavior Design Specialist, Stanford Lifestyle Medicine; adjunct professor per the lab's people page)
Emotion, not repetition, wires habits: celebrate immediately and a habit can form in days.
What it rests onHis stated mechanism and his unpublished program experiments (celebration vs no celebration) described on his references page.
Source: ideas.ted.com ↗
James ClearAuthor and habit educator · no clinical or research credential claimed
Habits form through repetition over weeks to months: expect about two months, with a real range of three weeks to eight months.
What it rests onLally et al. 2010 (median 66 days, range 18 to 254), which he reports responsibly including the range and the missed-day caveat.
Source: jamesclear.com ↗
Both address general adults installing ordinary daily habits; neither claims clinical populations. Fogg's evidence population is self-selected 5-day-program volunteers; Lally's was 96 university volunteers.
Nearly everything else: both say start tiny (fog-starttiny, cle-2min), both anchor new habits to existing routines (fog-anchor, cle-stack, with Clear crediting Fogg), and both reject willpower as a strategy. The disagreement is the mechanism and therefore the expectation to set.
Publication of Fogg's celebration experiments (he describes controlled comparisons inside the 5-day program and offers findings by email), or an independent trial comparing celebration-plus-repetition against repetition alone on time-to-automaticity.
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