Maybe it's happened to you. You recieve a bad grade, or you drop a food tray, or you forget the sugar at the grocery store. In response, someone says, "Oh well. Live and learn, right?"
This is true in many cases. Maybe the bad grade is due to failure to make time for homework, which you can learn to do. Maybe you dropped the food tray because you were trying to carry too much. Now you know to carry less. Maybe you forgot the sugar because you didn't keep a list, which you can do next time.
The aphorism, "live and learn" is helpful advice because it helps put a mistake, accident, or error into perspective. By definition, no one wants to make mistakes, but they're going to happen. And many mistakes, perhaps most, don't have an enormous impact on our lives. We learn from them and move on.
Live and learn is helpful advice when the lessons involved allow for opportunities in the future to do better. This includes tasks like homework, chores, and projects of many kinds. It may also include certain relationships like friendships and dating, especially earlier in life. As we live and make mistakes, we should learn from them lest we repeat the error next time.
But there is a limit to live and learn's usefulness. In some things, the most important things, you have to learn to live. Why is this so?
Driving a vehicle provides a helpful illustration. You can live and learn when it comes to little things about driving, such as how often you need to stop on long trips, how to preserve the brakes on your car, how to use cruise control effectively, etc. But the whole premise of a driver's license is that you have to learn to drive before you get out on the road. If you crash in a head-on collision because you were driving on the wrong side of the road, it's too late to live and learn.
Life is similar. Except that in life, Scripture makes clear that we are not starting out neutral or from a safe place. It's more like we are born in a car with no brakes careening downhill. Our life is the car and a fiery crash is certain.
Just consider some texts that indicate how dire our situation is before we do anything at all:
Ephesians 2:1–3:  And you were dead in the trespasses and sins  in which you once walked, following the course of this world, following the prince of the power of the air, the spirit that is now at work in the sons of disobedience— among whom we all once lived in the passions of our flesh, carrying out the desires of the body and the mind, and were by nature children of wrath, like the rest of mankind. (ESV)
Romans 3:9–12:  What then? Are we Jews any better off? No, not at all. For we have already charged that all, both Jews and Greeks, are under sin,  as it is written: None is righteous, no, not one;  no one understands; no one seeks for God.  All have turned aside; together they have become worthless; no one does good, not even one.” (ESV)
Notice the language in just these two passages: dead, children of wrath, turned aside, worthless. These texts apply to everyone from the moment of birth. Live and learn doesn't work in part because it presupposes a life to learn from that you don't have. The problem with live and learn at the most basic level is the hidden assumption that we are living now. In the sense of Ephesians 2:1, we are not actually alive at all. To live requires by definition the state of being live. Where there is no life, there is no living.
Now one might think that I am saying that we have to get from this dead and worthless state to a live and valuable state ourselves, but that is not quite right. The point I am trying to make is that what we typically think of living is not really living. It's something less than, something more dead than alive.
So how do we learn to live? We don't make ourselves alive; God does. That is precisely what Paul goes on to say in Ephesians 2:4ff. God makes us alive together with Christ. This is what it means to be saved by grace through faith: to be made alive with Christ. The Spirit convicts and regenerates a person, who places their faith (read: reliance) on Christ for their salvation and they are then given a new life to learn to live.
Following this, we have the language in places like Ephesians 4 where Paul reminds believers that it will no longer do for them to walk in the manner that they once did. They must now walk in a manner worthy of the calling to which they've been called (Eph. 4:1). They must no longer walk as the Gentiles do (4:17). Then comes the clincher in verse 21. Paul airs the assumption that the Ephesian believers have been taught to put off their old self (read: their old way of life inside and out) and to put on the new self. The main thing I want to leave clear is that the Ephesians had to learn to do so, and have to continue to do so.
This is why live and learn doesn't work. Paul makes explicit that we must learn to live because the life we once had wasn't really living, the life we now have has only just begun, and there's much to learn to do. So don't settle for living and learning. Learn to live.