Motorcycle racing is an outdoor sport. The riders are at the mercy of the elements. Not just the riders, but the teams and factories too. A bike that works well in the dry may be terrible in the wet. A bike that is strong in the wet may struggle when conditions were mixed. Finding the right balance when conditions change can throw the best laid plans into disarray.
All of these questions were multiplied by the weather at Assen. With nothing between the circuit and the North Sea but a row of sand dunes, the odd high rise office block, and a hundred kilometers of pancake-flat farmland punctuated by the occasional tree, the wind, sun, and rain blow out just as quickly as they blow in. The weather at Assen is as fickle as a pretty teenager in a crowded disco.
That made it tough for MotoGP at the Dutch circuit. Searching for the right setup was both perilously difficult and ultimately futile, for as soon as you found something in the right ballpark for the conditions, the rain would come or the track would dry out, and you would have to start all over again. Add in tarmac which has fantastic grip in the dry but diminishing grip in the dry, and you had a recipe for, if not chaos, then at least a fairly random mix of riders topping qualifying.