The amyloid elongation reaction can be quantitatively described by a "golf course"-like energy landscape model. Our finding that the TS contains a significant fraction of fibril-like contacts provides unique insight into the mechanism of misfolding. Such a state could be obtained in two ways; either by a rare collision compatible with the immediate formation of fibrillar contacts, or by extensive conformational rearrangement after the collision. However, only the former pathway is consistent with the requirement that the fibril end is unimpeded in the linear regime. Together this suggests that fibril growth occurs by a small number of collisions where the incoming molecule strikes the fibril in an alignment consistent with a strong, native β-sheet, whereas the majority of collisions lead to weak, non-productive interactions that dissociate much faster than the timescale of diffusive arrivals. Thus, the linear regime of fibril growth more closely resembles a "golf course" than the funnel-shaped free energy landscape of small protein folding . Once the first native β-sheet contacts form, the rest of the peptide rapidly adopt the amyloid fold . This portion of the process, where native contacts constrain the search of the molecule, likely resembles a canonical funnel . We formulate these observations in an energy landscape model in Figure . This model describes amyloid elongation in a manner consistent with findings from multiple studies in the linear growth regime and furthermore allows us to accurately define the absolute elongation rate of PI3K-SH3 fibrils solely from first principles (Supporting Material). Indeed, to our knowledge this is the first misfolding reaction for which it is possible to compute the absolute height of the free energy barrier. While our experimental characterisation was performed in the linear fibril growth regime, we may also consider our landscape model at high protein concentrations. The saturated growth regime can be rationalised by the end of the fibril having a significant population of partially-or incorrectly-bound molecules limiting further growth (Figure ). In this regime the fibril growth rate is determined by the time required to sample these kinetic traps. Similar to the linear regime, where growth occurs by rare, native-like collisions, the lack of long-range attractive interactions supports the golf course-like landscape with the distinction that the terrain surrounding the native target is much more rugged. These predictions are consistent with computational studies in the saturated growth regime . Our model does not necessarily predict a saddle-point in the misfolding pathway in the saturated growth regime and Φvalue analysis in this regime could further expand our understanding of the mechanisms of amyloid growth. However, due to the very high growth rates, such experiments will face significant practical challenges (See Methods).