Like the golden opportunity presented by The Simpsons for major stars to take on one-off guest-starring roles, there's probably a temptation to imagine that the chance to appear in a cameo in a Marvel movie would be too good to turn down. How else could you explain the fact that Matt Damon appeared for a grand total of about 40 seconds in Thor: Ragnarok?
And while there have been some pretty incredible special appearances over the past decade - including Hollywood superstars and politicians - there could have been more. Whether thanks to real-life circumstances or story changes, some of the initially planned cameos for famous faces and recognisable characters ended up not making it much further beyond the planning stages.
Stunningly, some of the names lined up for cameos proved that the MCU actually isn't the irresistible juggernaut it sometimes appears to be. Kevin Feige might be hoovering up most of Hollywood's most impressive - and most expensive - talent, but he couldn't get everyone his directors wanted to agree to appear.
Just ask David Letterman...