Today I spent a frustrating 45 minutes (the reason's not important) trying to recall the name of this man:
I could tell you anything else about him - that he spent 27 years in prison as a political prisoner; became South Africa's first black President, was played, in the film Invictus, by Morgan Freeman, and many other things.
But the name 'Nelson Mandela' simply would not come to my mind.
This happens me from time to time; it's something I call 'Brad Dexter Syndrome', after the actor who played Harry Luck in 'The Magnificent Seven' and whose name I always had trouble remembering (with apologies to Mr. Dexter) when asked to identify the cast of that film.
And I hate when it does, because I have to stop myself from resorting to the Web to find the name of the individual concerned because I'm determined to recall it for myself and not rely on external assistance.
I did some research into the cause of such a memory block (and that's what it is, not some form of incipient dementia) and there was a suggestion that it can occur as the result of stress, or of active memory centres of the brain preventing retrieval from other areas (I'm an interplanetary adventurer, not a neuroscientist, so I'm not even going to attempt to analyse that).
But invariably the name (and it's always a name, never anything else) comes to me, even if I have to use a more circular approach to find it.
It doesn't happen often, but damn, it's annoying...