The Machiavellian Lawyer once said:
To excel in a law firm, make yourself indispensable. Start by identifying a type of knowledge within the firm that is highly-valued but in short supply. Exploit this shortage by making yourself an expert. Then leverage the value of your new knowledge by becoming involved in as many projects as possible.
After you have become an expert, think twice before teaching your skills to others. If you share your knowledge too freely, you will devalue the currency that has made you rich. When called upon to instruct others, learn the secret known to every Italian cook: share your recipe willingly, but omit a minor, yet important, ingredient. The cook’s students will be able to replicate the dish but will never be able to duplicate it. The cook will remain the master.