Lost On The Way
Science is not only theory but also practice; and as such it always stays close to reality and experiences. Its theoretical part, however, is permanently in danger of losing contact.
So, for example, while trying to realize the idea of one single all-embracing system constructed from few simple building blocks: sooner or later its complexity must get out of hand. Endless chains of deduction lead to no concrete results. The truth, that should be granted by them, gets lost on the way to realization. For it cannot enter the scene but from the other side, from reality, through experience.
Existence need not be justified. It appears. Beyond any reasoning and description. But, surely, not without reason and the proper circumstances. Not outside its space, as we will say.