That's right, I said it. A little bit of knowledge is a dangerous thing. On the contrary, a lot of knowledge is a good thing. Also, no knowledge can be a good thing. Let me explain.
I'll use a recording studio as an example. If you're a musician, odds are you've been advised that "no mic will sound good on that amp unless it's an SM57, and it has to be positioned at this spot." This statement completely negates the fact that mic placement dramatically changes the tone of a mic, and the room an amp is in also plays an important factor. Also, different mics have different characteristics, so how do you know that you're not passing up the tone to end all tones by trying some different mics if all you do is demand an SM57?
To put it bluntly, there's a reason you're a guitarist and not an audio engineer. An audio engineer will know these things and know how to get the sound you desire while coming up with some unique and interesting tones. All you need to do is sit back and give the audio engineer a little faith and room to breathe.
On the flip side, someone with tons of knowledge on the topic knows that the engineer knows what they are doing and tends to just trust it. The same is true of someone who doesn't know anything, as they may not even know what an SM57 is! People in both of these categories are more willing to accept the proven fact that the gear doesn't make the record, the engineer makes the record. Someone who has a little bit of knowledge, but doesn't really know what the hell they are talking about, tends to get hung up on the gear the engineer is using rather than the end product that has been presented to the client in the sales meeting.
The same can be said in a variety of industries. I'm using a recording studio because this is what I know, but I've also witnessed it when discussing marketing campaigns for artists. The artist gets an idea of what it will take to get somewhere, but your marketing knowledge says that won't work. Despite this, the artist acts like you don't know what you're talking about because they are armed with a little bit of knowledge on the topic and think they are right. I've encountered this situation many times over the years.
The biggest problem with musicians who possess a little knowledge is that they tend to be counter productive. They start fights, create tension, and are constantly being combative. Obviously, this isn't the same in every case, but in many cases that I've encountered it has been the case. What I'd like to see, but rarely do, is an artist who has a little knowledge but they know they don't know everything and henceforth are willing to sit back and absorb what they can from your professional knowledge of the subject.
So if you're working with someone who has shown proven results, but you're finding yourself questioning their every move, try to take a step back and let them do their thing. Odds are that things will go smoother if you have a little faith in them.