“He who has a clear idea can also express it clearly.”Georg Christoph Lichtenberg · Caietele de însemnări · 1799 · Caietul K, însemnarea 22
If you can't say it clearly, your idea isn't ready yet — clarity is the test of understanding.
Lichtenberg reverses the usual excuse of people who speak vaguely. Vagueness is not a stylistic flaw but a signal: the idea itself is confused, incomplete, or contradictory. Clear expression is the test of understanding. When someone tries to explain a decision to a friend and keeps stumbling over sentences, they usually discover they do not yet know what they want. Writing simply forces thinking to be finished.
Why it matters Useful to anyone who writes, teaches, or leads: if a message will not come out clearly, the thinking is unfinished, not just the phrasing.