If you plan on contending, you've got to be able to hit it long and straight off the tee, under pressure. According to Golf Digest Teaching Professional David Leadbetter, "Your driver is the most important club in the bag (except maybe your putter) because it sets up so many shots."
If you don't have the big stick under control, your confidence in the rest of your game will inevitably decline. Work on hitting the longest club in your bag well. If you can, all of the other clubs in your bag can't be too far off.
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