I think the reverse psychology approach is most effective as motivation when (A) the task is described as hard, but also (B) there is no direct implication that

I think the reverse psychology approach is most effective as motivation when (A) the task is described as hard, but also (B) there is no direct implication that you can't do it. I was trying to think of some impressive sounding examples when someone-said-I-couldn't-do-something-but-I-did-it-anyway but I can't think of any. It's more common that (A)+(B) occurs for me.