A single self-portrait is an oddity — a titillating peek into an artist’s private life or self-conception, bu t otherwise no different from other figurative paintings. But when you see about 70 of them, by more than 30 artists, in “The Self-Portrait, From Schiele to Beckmann” at the Neue Galerie, you start to notice that this narrow genre has a universal scope. It’s a consciously constructed illusion of spontaneous self-revelation, a sincere put-on. And as such it’s a peek beneath the hood of art in general.

Like most shows at the Neue, this one is tightly focused on German and Austrian painters from the first half of the 20th century, combining museum-owned works by the famous Egon and Max of its title with lesser-known loans, like Paula Modersohn-Becker’s memorably odd 1906 “Self-Portrait on Her Sixth Wedding Anniversary.” But the curator, Tobias G. Natter, sets the stage with a handful of earlier European art works, including six wonderful small Rembrandt etchings.

In five of these, the Dutch master renders himself with eyes facing forward, as if staring into posterity. But in the sixth and latest, “Self-Portrait Drawing at Window” (1648), Rembrandt shows himself as he actually would have looked, with the slightly worried face of an artist at work, his eyes averted. It’s because he’s referring to a mirror, of course, but it also evokes the fundamental difficulty of attending to oneself and someone else at the same time.