For non-designers (and immature designers) the toughest part of design is trying on different trade-offs.
The reason it is so tough is this: while most people can shift between ideas with relative ease, it is harder to shift between conceptions — different logics of coherence and meaning that invest ideas with different significance.
Harder still is to allow new conceptions to animate perceptions. Old conceptions cling and highlight features of perception that would remain inconspicuous to fresh eyes. And each shift in design direction adds new relevancies without removing the old ones, so the problem becomes more insoluble with each iteration.
It is like memory: it is easier to learn on command than to forget. The old ideas, once seen, become hard to unsee. The old concepts, once learned become impossible to unlearn. Perception becomes almost cubistic — too many simultaneous perspectives are viewed at once.
Pluralistic play — the ability to flit between logics — to try on different conceptions and perceptions — this takes years of practice, and the practice can only start once a person has discovered the dimension of mind that multiplies the universe into innumerable overlapping everythings.