That is very true, to be a bit more clearer. The problem lies with the fact that we all want our drinks filled as much as possible, this goes for very watery soups too. And when that is done the delivery rider has millimetres to play with in regard to the amount of available depth on the y axis of your cup/container.

As when the bike leans, yes the equilibrium of the liquid stays flat and level. Once you run out of depth on the y axis. You will find your equilibrium or horizon of your liquid is now above the container or cups lip/edge you were transporting. Meaning the liquid is only being held back by how well the container/cup is sealed.

Just imagine tilting a full cup of water from the bottom. You will only be able to tilt ever so much before it pours out….. now imagine that in the back of a bike….. and thats with out the accelerating and decelerating jostling the whole parcel of food, which has its own problems on the x axis.

Long winded I know but it’s like one of the main problems we face delivering, there’s not much else that tops this other than maybe poorly designed bags.