On Things Seeming Obvious Once You Know Them

There's a complicated mess of wires, most connecting several of the five metal boxes, amongst others which are just loose ends dangling, that together make the system you're working on.

There's a phone connected to this complicated mess that puts the system in configuration 1. Your task is to put the system in configuration 2 by reconnecting the phone to a different port. The problem is, no one is around and you don't know how or where it's supposed to connect. But as soon as you have the right connection, the system will tell you it is in configuration 2. So you go on your journey to figuring it out:

• Hit and trial
  You start off by disconnecting the cable connecting the phone to the system. So now you have a phone connected to a cable with a loose end, and you have to figure out where it fits. 
  You start looking around. You have no idea where it goes, so you make a quick scan of all the ports, but find nothing that the wire could connect to.
  
• Break it down
  You grunt and then pause to think. That's the next logical step after having blindly tried to solve it. So, you break the problem down.
  You eliminate each box one by one: 
• The box connecting to the monitor doesn't make sense.
• The box connecting the CPU makes sense, but there's no port there, and so on. 
You've now checked and eliminated each one of the big boxes, but you still find nothing. You then look at the dangling wires, but there are too many to check all, so you go through some, and then skip the rest.
• Think of what you know
  You pause again. You've checked all the boxes, you've looked at the cables, surely the wire has to connect somewhere. Stumped, you list out all the things you know:
• You know your co-worker from yesterday connected it. 
• They also didn't take more than a minute, so it's easily accessible. 
• You also know that the position of all the boxes is exactly the same as it was yesterday, so that means the wire doesn't have to connect to an obscurely located port.
• Change your angle
  Baffled, you sit down. And then it strikes you!
  There are two ends of a cable! And in a hurry, you started off by disconnecting the end connected to the system. 
  So, you stop looking for the port that the loose end of the cable connects to, and instead, start looking for a loose wire that can connect to the phone. 
  You find it. It's been right in front of your eyes the whole time!
• In Retrospect
  Smiling, rather embarrassed with yourself, you look back and think this was so simple.

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Things seem hard, sometimes frustratingly hard, when you don't know how to do them. And nearly always, they're entirely obvious once you know how they work.

Does that sound familiar? If not, solve this:
You're at a 200-meter cliff. You have a 150-meter long rope, and a small knife with which you can cut the rope. There is a hook around which you can tie your rope at the 200-meter (where you currently are), and one at 100-meters. How do you get down to the bottom safely? 

Yes, you're wearing an orange bow tie.

And no, there are no clever knots or fancy tricks involved. There's a simple solution that'll seem obvious once you solve it ;)