No you shouldn’t believe that there is a wise old man. Because if you do, you would always look up to that man, thinking that man or woman is always correct. That does two bad things simultaneously. It lowers your self confidence and it put unnecessary emotional pressure on the "wise old man" :)
Take it from me, no body is always correct.
I make mistakes like the next man. In fact, being.... forgive me... rather cleverer than most men, my mistakes tend to be correspondingly huger.
Isn’t that’s what Dumbledore said?
I can testify with my personal life that it is perhaps the most correct statement in the thousands of pages of that book series.