What's your best/worst "Told you so" moment in IT?

Personal story

> Set up some infrastructure to complete a job
> Supervisor insists it won't work and we need to do X instead
> I'm pretty sure X is overkill and refuse
> Eventually we meet in the middle at Y, which is still a bit overkill but at least we can compromise
> Get Y almost done, supervisor insists Y will not work and we need X
> Lots of back and forth before I'm finally worn down and agree to do X
> Implement X
> It doesn't work
> Talk with other industry professionals
> They all insist the first solution is best and X is overkill
> We go back to the first solution
> 1 month wasted :/