It's difficult sometimes because I have trouble "keeping up" with extroverts and their high energy levels. Let's say that I have a day off work. Should I stay home where it's quiet and peaceful and re-charge my batteries (that's the same for us introverts as "going out and doing something really fun" is for you extroverts), or do I spend my day off doing something that will essentially drain my batteries - and then be at work the next day wishing I had taken the proper time to recharge like I knew I should have?
The reason I say it's difficult is because I want to "accomodate" my extrovert friends. And I want to keep them. I really do value them. But, when I run out of "juice", I'm not very much fun to be around. And I look into the future too. If I have a day off, but I know I've got a really long week ahead of me, I know that I should be wise and take the opportunity to recharge while I have it. It's not that we want to offend anybody (and we know it "looks" selfish and sometimes it is selfish), but you just have to look at it knowing that we have to take care of ourselves before we can be any good to anyone else. I know for me personally, when my batteries are drained, my fuse is extremely short. I'm not fun. I get really cranky.
When the batteries are fully charged, I have a lot of energy and can do a lot of things, but if it's a "high octane", high energy environment, it can deplete the battery kind of quickly (sometimes as little as, say, 2 hours!). Other times, I can go somewhere for 3 or 4 days with someone, provided that I have some breaks in the action here and there. It depends on how "demanding" the social environment is and also if I came into the situation fully charged or already on low.