That, very obvious, statement is actually an insight that two types of people tend to miss.
Those people that allow the unknown to stop them from moving ahead; and
Those people who don't recognise they could do with some help.
"It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." Mark Twain
For many people, perhaps even the majority, this is just a fact of life, but for those who struggle with this statement here are some thoughts for you:
Whatever it is that you don't know, someone else does.
Lots of people have overcome this very same "unknown" and gone on to be very successful ... so you should too.
Experience is a wonderful tool ... if you can take advantage of someone else's experience that is a very smart thing to do.
Be wary of advice from people who have not been there, done that ... there are many people who just love to give advice, whether it is good or not.
Be wary of advice from people who have been there, done that and clearly still not learned "the answer". If you pay attention you will understand.
Seek out those with experience.
You don't need to accept the word of any one person ... in fact if you can get more heads onto the subject, all the better.
Asking for help is actually a sign of strength ... not weakness. Not asking can be a sign of ego, stupidity, misplaced pride or just naivety.
Recognising and accepting that you don't know something is not always easy.
If life was easy then everyone would do it ... so if your problem was easy then likely you wouldn't be in this position.
Self awareness is always a good trait to work on.
"I think self awareness is probably the most important thing towards being a champion." Billy Jean King
Everything said can be applied to your career, your business, your social life or just about any part of your life.