The principle
Conserve your energies by keeping them concentrated at their strongest point. You gain more by finding a rich mine and digging deep than by skipping from one shallow source to another.
The application
One deep relationship, one deep skill, one deep project is worth ten shallow ones. The professional cost of staying spread thin is not exhaustion — it is forgettability.
The defensive tell — how to spot it being run on you
When a senior person at your company makes a sharp narrowing move (kills three side bets to pour everything into one), they are not panicking. They have computed where the leverage actually is. Watch what they kept; that is the signal.