What is something that you feel most 2nd lieutenants lack?

Respect for subordinates abilities and leadership..and that other than for that bar on his shoulder..a lt could be handed his hiney back on a platter..the military is a artificial fabricated bubble. Dont let it go to you head.

Most prior enlisted and especially combat veterans who make officer . Many would follow into hell armed with a water pistol..if your not one. Dont try to be..learn first.

Experience. That's it for the most part. The only real curable difference between a new LT and a seasoned officer is the experience they have procured.

Respect and expectations.

Nothing.

We somehow forget that Lieutenant's need to be trained much like the new Privates, and need to be given room to screw up much like new Privates.

As much as we deride Butter Bars...they are still trainable. Just need a good NCO (or Petty Officer as the case may be) to tell them how things REALLY work outside of school.

Most LTs in general, lack experienced are over compident.

I think they lack experience and the understanding of enlisted life. Now obviously these dont apply to all 2LTs as I've had phenomenal LTs both in the Army and Marine Corps.
The experience is gained over time, but the understanding can only be gained by talking to your soldiers, and ditching the sense of entitlement and supreme know all mentality that I've seen from new 2LTs far too often.
If I could give one piece of advice to newly commissioned 2LTs it would be, respect is reciprocal. Your enlisted counterparts will respect your rank, but they will not respect your leadership until you respect them and their experience.

Experience like all new soldiers.

I certainly lacked perspective. With little experience and cursory training I was self centered. Pilot training provided a 1-year buffer between university and the real Air Force. Even then the real Air Force was very different than I expected. My first lesson: if you want something you have to ask for it.

Life experience.