Basic spawn function won't work?

I was messing around with coroutines/spawn in ROBLOX Studio, and this script happened to not work.

There is no errors being printed in the Output.

The hint just keeps being destroyed and created endlessly. No numbers are being printed in the Output. The value that a is should be printing every second.

local a = 0

function myNewThread()
repeat
    local h = Instance.new("Hint", game.Workspace)
    h.Text = "This is a hint!"
    wait(1)
    h:Destroy()
    wait(1)
until
    a >= 10
end

spawn(myNewThread())

while true do
    a = a + 1
    print(a)
    wait(1)
end

Thanks in advance.