On any mechanical repair job ego comes in for rough treatment. You're always being fooled, you're always making mistakes, and a mechanic who has a big ego to defend is at a terrific disadvantage. If you know enough mechanics to think of them as a group, and your observations coincide with mine, I think you'll agree that mechanics tend to be rather modest and quiet. There are exceptions, but generally if they're not quiet and modest at first, the works seems to make them that way. And skeptical. Attentive, but skeptical. But not egotistic. There's no way to bullshit your way into looking good on a mechanical repair job, except with someone who doesn't know what you're doing.