Falling down properly is good Defense. In any real fight, you are probably going to take a few hits, probably going to get hip-checked into a wall, and very possibly thrown or tripped to the ground - especially if you are ambushed - and definitely if you are ambushed by multiple attackers.
If you fall properly, you probably won't shatter your elbow or knee on the concrete, taking yourself out of the fight. If you fall properly, you can probably survive a hip throw - even from a strong Judo practitioner (Yes, Virginia - their hip throws are often more punishing than what you see in MMA matches.) When you fall properly, and add a good roll, you can usually get back to your feet and continue the fight.
The next lessons are Defensive - how to protect your neck. Protect your back. How to avoid giving up an easy armbar. How to stay awake and alive. How to protect yourself from attacks without being destroyed.
But good D is also laying the ground before the attacks - putting yourself in the strongest possible positions to defend. Because attacks are inevitable, especially from the desperate and the weak. Be in a position to defend when and where it matters, on your terms. Learn to determine which attacks require first response, which attacks are meaningless, and which attacks are best engaged and defeated on your own timeline.
Then you need to work on getting your wind up. The first guy to run out of gas usually loses. Build your staying power.
"Can you show me the omoplata?" Sure I can - but if you don't have good D, good wind, and one of the most important traits of a Warrior - patience - knowing the omoplata is useless to you. Patience is one of the hardest skills to teach, especially in the martial world. If you are not patient enough for your enemy to make a series of mistakes, and strong enough to stay in the fight long enough, you'll never have the opportunity for an omoplata.
In Combatives the easiest path to victory is often to let your enemy decide what techniques you will use. Why go for a knee lock if he's leaving his neck open? Why take the armbar now when you know you are only a few moments from breaking his spine and having him sh*t himself?
And before you run to look up the omoplata, here's one of the most important tips I can give as relates to the martial endeavors - when your enemy is making a mistake, do not interrupt him.
Remember your Ōishi.