A common problem
encountered when first observing dark nebulae is "Are you looking at
the right object?" For dark objects, this questions is more vexing
than when looking at typical light-emitting objects. Dark objects have
even less contrast than against the background night sky than dim
stars.

I have never understood how a visual observer could claim to "see" a
dark nebula. If all you are seeing is an absence of stars, then you
might as well be looking at some star-poor region of the sky, and any
attempt to observe a dark nebula will automatically be successful.

If the dark nebula is instead delineated by it bordering against a
bright nebula, then the observer is "seeing" the bright nebula rather
than the dark nebula.

For those who claim to have "seen" dark nebulae, what is it that
constitutes a successful or unsuccessful attempt?