Humility > Arrogance
Being a consultant means that sometimes, unfortunately, you have to do some ass-kissing. When a product manager at a major corporation tells you that they’re having a hard time using a feature you built and claims that “it’s buggy”, you should ask them if they have time for you to demonstrate the feature and ask them how it can be improved. Opening up this line of communication strengthens your relationship with the client and shows them that you are easy to work with. Your first response should never be, “It’s not buggy.” I have never used the phrase “it’s not a bug, it’s a feature” seriously with a client; I use it very jokingly with colleagues.
A consultant’s job is to provide a service to their clients and listen to their needs. You sometimes have to put aside arrogance if you want to keep getting work. The easier you are to work with, the happier your client and colleagues will be.
I'm not saying that the customer is always right, but that you’re not correct all of the time either.