I recently came across the single curve problem that states that we need differenct curves for discounting cashflows and projecting forward floating rates.

On google I am not able to find a proper article about it, so could somebody tell me what exactly the problem with having only one curve is?

What I found out so far is that it has to do something bith the FX basis or different tenors and that with one curve we cannot reconcile the market. But what markets or whar exactly cant we reconcile? I'd be very happy if someone could shed some light into this.

Thanks a lot!