Subject with the most impact?

On Those Big Words we (mostly you ) are talking about such a great variety of informative subjects.
At least I can conclude we have all a base of knowledge that we built day to day. From the moment we were born, till this exact time.
So the question that arised from me was:

What is the most important lesson you learned in life? Ore what is the subject that made the most inpact on you of all time?

Hard question. I suppose learning to read must be high on the list of important lessons, for without that all else is largely closed

FionaK: I like your answer, its not what I expected. But I think you made a good point. Communication is an important thing. The beauty of "sharing" thougts. The beauty of categorizing, naming things, and being aware of them at this point. The key to receive knowledge from, made by or shared by other beings.

Vninect: Yes its one hard question I think myself. Im curious what you will come up with (maybe) at the end of this week.

Myself I dont have a definitely answer, cause maybe tomorrow i come up with an better one, ore an other view. But I came up with this that is at least high on my list.
For me maybe it is: The knowledge of that you just dont know.
I know it contradicts. But yet it allows me to have an open view(as far as possible, Im still an human).
But I hope this wil help me receive information more purely, and judge less. Gife me more points of view.
There no certainly. It gives you freedom, sometimes maybe to mutch for an human mind. But you can still believe.
I still believe in natural science and stuff. It gives stabillity. but I just let go the stiff hold of knowing.

I like you.

I'm not sure what I'd say the most impactful lesson is for me, but the first one to come to mind is based on the deceptively simple truth that actions have consequences.

It seems so obvious, yet it's a lesson children have to learn at some point. Its import quickly fades away, as it is learnt at quite an early age, one which by the time subjects like this can be discussed intelligently is largely gone.

Because the lesson itself is forgotten, even if what is learned may remain as part of ones world view, this idea seems to be relegated to a "common sense"-truth, hidden away in plain sight as it were. Essentially, what seems to remain, is this: "if you do bad things, bad things will happen". That's become part of culture, part of social norms, part of justice.

...left this post for a bit, and forgot where I was going with that. But yes, realizing that you hold the power to affect your life, that's important.