Should a consultant know everything?

Although I am often asked to do some consulting and like helping people, my two consulting jobs left me with a strong opinion that I do not like to be a consultant.

Recently, I mentioned this fact in a professional conversation, and the reaction was somewhat unexpected. The conversation went like this: yes, some people feel uncomfortable consulting because you are expected to know everything, and then they are afraid that they will get a question to which they do not know the answer. But if you work for a consulting company, you do not need to worry about that because there are always others you can ask, and somebody will know. And the customer does not need to know that you used other resources. 

I never thought about consulting that way because I never saw it as a problem that I might not know something. It is perfectly normal not to know everything, even in your narrow field. I never have a problem saying that I am unsure about something and need to look it up or ask people who might know better than me. I do not think that ever compromised my credibility. Moreover, I would be more suspicious of someone who always has answers. 

Once, I interviewed a person for a Postgres DBA position and asked him to rate his knowledge of Postgres on a scale from one to ten. He said: seven. After he was hired and completed his first one hundred days on the job, I asked him at our one-on-one how he would rate his knowledge of Postgres now after he had learned so many things. He said: now it it indeed seven! At his first end-of-the-year review, I asked him the same questions. He said: oh, now, it is truly seven! 

To be honest, I often want to give myself seven in Postgres as well. Definitely not more than eight 🙂 

What do you think? Do you expect a consultant to answer all and any questions you have? How do you feel if they “need to look this up?”