3 things I wish I had known at 18

The other day someone asked me what I wish I had known at 18. I wish I had known a lot! But, a few things immediate sprang to mind.

1. Have a long term plan. When I was younger the sky was the limit and looking back on that time I realize that I really didn't think very far out. I would make decisions based very much on the short term without really thinking about how that decision would play out in the long term. Having a written out, long term plan would have been immensely helpful.
2. Have humility and listen more than you talk. At 18 I knew it all. Knowing it all makes you a terrible listener and pride is a great setup for a fall.
3. Relationships are precious, fragile and require more care than you think. I just assumed that relationships were easy because many of mine had been up to that point. In my young adult life I took too many relationships for granted and didn't show enough effort and appreciation towards people that were important to me.

What do you wish you knew when you were 18?