The years of searching in the dark for a truth that one feels, but cannot express

These were errors in thinking which caused me two years of hard work before at last, in 1915, I recognized them as such... The final results appear almost simple; any intelligent undergraduate can understand them without much trouble. But the years of searching in the dark for a truth that one feels, but cannot express; the intense desire and the alternations of confidence and misgiving, until one breaks through to clarity and understanding, are only known to him who has himself experienced them.

Albert Einstein