You have to look at the big picture here.
You can't just get caught up in where you are right now,
although that is the trap that we all seem to get caught up in.
Can someone explain me the underlined parts?
Big picture - you have to look at the whole situation. This could mean long-term effects as well as short-term, how other people will be affected as well as just yourself, possible negative effects as well as positive, etc.
Caught up in where you are right now - thinking only of whatever you are involved in at the moment. This sounds like it's referring to the person's emotional state a bit as well.

Proponents of recycling and other "green" solutions sometimes fail to see the big picture. Depending on how far the materials to be recycled must be transported and the method of recycling used, recycling can often consume more energy than it saves.

I know it seems like Sarah is behaving selfishly. She's totally caught up in where she is right now---all she can think about are the wedding plans. She seems to forget that after the dream wedding, comes not-so-dreamy married life, and neither she nor John has a decent job. I don't know what she thinks they're going to live on.
Thanks, Delmobile!