What were / are your biggest knowledge gaps between the military and civilian worlds?

The one thing I tell Veterans that I help out is stay focused!  Much like what Quentin said already, there are a lot of hurtles in your path as you transition but these can all be cross if you stay focused.  Understand that you are entering a world that understands little of what you just went through for the past 4, 10, 15, 20+ years.  Be honest with people and don't sale yourself short.  The skills that we picked up while in the service cannot be taught in the classroom.  Our ability to think on our feet, asset the situation quickly and resolve the problem in a timely manner are all skills regardless of your branch, number of deployments, medals, whatever that we all share.  

There are three things that I would tell someone that is about to leave the military; stay motivated, be flexible, and learn the lingo.  I assist veterans in my community to gain employment and receive benefits, and these seem to be the biggest three hurtles for most.  The fact is that in the military there is a strong support chain that keeps the members focused and driven, and this can leave some ill prepared to deal with the reality that on the “outside” all you really have is you.  This can be very hard on some and a lot of veterans find it easier to give up than to keep driving on. Or even worse I have seen many veterans turn down opportunities that were not what they felt they should have been offered.  What veterans have to keep in mind is that the great things that they have done in the service are wonderful, but that does not exclude us from proving ourself in the corporate word. We have to be willing to take any opportunity offered and turn it into the opportunity that we want it to be.  And veterans do have a lot of skills and abilities that are in high demand in the corporate sector; I have found that they just don’t know how to market those skills and make themselves employable.  Learn the terms and what they mean and how it is applied in the workforce,  most are surprised to find out how much they already know.  Over the past two decades the military has been very intertwined with corporations and how they do business, corporations just use different terms.

While everyone seems to support the troops, they really don't care how you did it in the military. Forget what you know and be willing to learn how it's done in the "real" world.

Civilians want someone who is going to fit their mold and don't want to change to a militarized way of doing it.

Many civilian workers work hard and have good work ethic yet they may seem undisaplined because their was is unconventional.

Get used to a time clock! Don't clock in early or leave later than whatever you are scheduled. Overtime costs the company money. They may want you to finish tomorrow or work faster to get done on time.