The sincere alone can recognize sincerity. Not a Hero only is needed, but a world fit for him
 Thomas Carlyle, On Heroes, Hero-Worship, and The Heroic in History (1841). copy citation

Context

“the world has truth in it, or it would not exist! First recognize what is true, we shall then discern what is false; and properly never till then. "Know the men that are to be trusted:" alas, this is yet, in these days, very far from us. The sincere alone can recognize sincerity. Not a Hero only is needed, but a world fit for him; a world not of Valets;—the Hero comes almost in vain to it otherwise! Yes, it is far from us: but it must come; thank God, it is visibly coming. Till it do come, what have we? Ballot-boxes, suffrages, French Revolutions:—if we are as Valets, and do not know the Hero when we see him, what good are all these?” source