Under normal circumstances, a thing is forgotten only by occupying the mind with something else, i.e. by losing interest in it through acquiring interest in something else. A thing cannot be forgotten by simply willing it to be gone. Loss of long term memory can result from damage to the brain, a faint original impression or agitation or excitement of a moment. A second type of forgetfulness is simply refusing to bring it to consciousness. For many a war or other tragic experience is dealt with this way.
If you're wondering if you left the electric iron plugged in, you did.
If you're wondering if you took the meat out to thaw, you didn't.