I thought you said...
One of my biggest pet peeves has to do with people who don't follow through on their commitments. When someone says they're going to do something, generally speaking I expect them to do it.
Obviously there are exceptions to this, but I'm talking about a general rule.
When you plan certain aspects of your life around what others say, it's incredibly irritating when they don't follow through. It is even more frustrating when because of this, it causes you not to be able to meet your commitments.
Some people have also then become notoriously good at not ever committing to anything. This absolves them from any responsibility and allows them to either do or not do based on a whim.
I would suggest that you don't allow yourself to fall into either of these categories. It will speak volumes for your character that you not only follow through on your commitments but that you are also not afraid of making commitments.
The bottom line: Do what you say you're going to do, be able to say what you're going to do.