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Relevant quote:
Secondly, before the 3 seconds have elapsed the object may have already been destroyed (for example, if it reached
Workspace.FallenPartsDestroyHeight
). In this case, the code would error as it tries to destroy an item that has already been destroyed.
This is wrong. You can freely Destroy something that has already been :Destroy()ed. Destroying something that has already been Destroyed won’t cause an error.
This can be tested easily:
local p = Instance.new("Part")
p.Parent = workspace
p:Destroy()
p:Destroy() -- No error.