After changing the plane tyre, a bolt wasn't removed so landing gear couldn't retract

[AEROMEDIC]

If that procedure does not also ask you to check the pin streamers for condition and legibility including the attaching rings, then it should.
They are there to help you identify the landing gear pin status i.e. removed or installed.
It's the little things that can start "big things unravelling".

[Dan_Brown]

Having Gear Bolts/Pins on the pre start checklist, would be a step in the right direction. Belt and braces. Or is it "hurry up, we have a schedule to keep"?