For all but one in thousands the goal of their thinking is the point at which they have become tired of thinking.
 
[Tausenden für einen ist das Ziel ihres Nachdenkens die Stelle, wo sie des Nachdenkens müde geworden.]

Gotthold Lessing (1729-1781) German playwright, philosopher, dramaturg, writer

Letter (1771-01-09), to Moses Mendelssohn
    (Source)

(Source (German)). Alternate translations:

In a thousand cases to one, the goal of reflection is set at the point where one gets tired of reflection.
(Source)

For the vast majority of men, the object of their reflection lies at the point where they become tired of reflecting.
(Source)