I came across this chair at my university that had its back falling off. It'll take a long time before it's properly fixed, or worse still, they'll toss it and replace the entire thing, so I wrapped some tape around and it's very solid now!
I have some duct tape folded around an old card in my wallet and used my victorinox knife to cut it.
Such adhesives are not good in tension like that. It holds for a moment, but gives way when the load is applied for a longer duration. This could be dangerous with a chair.
@Eheran There's a metal bar right behind the back that notches in, so the pressure goes there. The tape is just stopping it from sliding downwards. Thanks for pointing that out though.