The hardest-learned lesson for any young consultant is how to be wrong. After all, you're the expert, right? But we're all painfully aware of our own limitations; otherwise we'd be in sales!
It's important for a good consultant to acknowledge and admit his limitations. It can even become a sport! Once you're gray enough, you can plead ignorance to almost anything and still get the gig!
I once admitted to the client's main point of contact that, until that meeting, I had never even heard of the product I was developing requirements for! Never mind that I knew it pretty well; I just wanted to see what he'd do! Of course, he kept the project going. After all, he had picked our firm…
But have you ever noticed that the client is almost never right? In fact, it's fair to say that the client is always wrong about everything, from requirements to the final punch list.
This may just be the hardest-learned lesson for an old consultant to face: You're going to tell them one thing and they'll do whatever they decide anyway. The best you can hope for is to convince them, through and through, all of them, that your way is best.
If you can't get real heartfelt buy-in, you're just as bad as they say consultants are!
Whatever. You know we're all even worse!