Select Trim and you’re asked to select the cutting object and then the object to trim. Select Split and you’re asked to select the object to split and then the cutting object. I’m old and easily confused; why not the same selection order for both?
(And on a related subject which I’ve mentioned before - as well as Trim cutting back to the cutting object, could Trim be made to extend objects to the “cutting” object? Then if you’ve got several lines which have to end at another [for instance] Trim will both extend the ones that fall short and shorten the over-length ones in one command).