There is a lot of misinterpretation about this concept, which tends to reduce the problem to a "conservative vs progressive" debacle.
A modern equivalent of his thought is the Lindy Effect [1], where every day a non-perishable thing survives (an idea, a technology, or in the original example, a Broadway show) adds another day in its expected survival.
Simply put, the longer one thing lasts, the longer it is expected to last. The fence is his metaphorical way of saying that what may be holding a change (thus, a fence) may have its reason and its strength is positively correlated with its lifespan.
A modern equivalent of his thought is the Lindy Effect [1], where every day a non-perishable thing survives (an idea, a technology, or in the original example, a Broadway show) adds another day in its expected survival.
Simply put, the longer one thing lasts, the longer it is expected to last. The fence is his metaphorical way of saying that what may be holding a change (thus, a fence) may have its reason and its strength is positively correlated with its lifespan.
[1] https://en.wikipedia.org/wiki/Lindy_effect