Just one? If only it were that easy!!! For someone like me, the list is practically endless, and goes all the way back to my childhood.
I'll admit it, I'm terrible friend material, in terms of the day to day, staying in touch, social type stuff. When one of my "down" moods kicks in, I retreat from human contact, general with no explanation. And when the mood passes, I feel so bad about disappearing on everyone that I can never find the words to make it right again.
But what I usually try to get across to people who matter to me, from the very beginning, is that while I may SUCK at that sort of stuff, I am SUPER a being there for others when they need someone to listen, a shoulder to cry on, actual physical help with something, prayers, or anything along those lines. If I tell you I'm your friend, you can count on me for that sort of thing for the rest of your life!!