One of the things that I value most is integrity. I don’t mean it so much in the ethical sense, but more towards truth and reliability. You might think of it along the lines of “I am my word”.
Because of time. It is probably our most valuable resource. Yes, your health and your mind matter quite substantially too, but at least with time you can work on both of these. Without time, you don’t have the power to change anything.
So, as you might imagine, I highly value my time. Minutes, hours, days wasted could have been spent doing more productive, rewarding or exciting things. As a result, when I say “I’ll be there at 7:00pm”, I mean it. This is because I believe that another person’s time is no more or less valuable than my own. I do not believe that I have a right to waste one of their most precious resources by making them wait.
Or, for example, if I say “I’ll get that done”, I mean it. This is because I have created the expectation that something will happen, from which another might make plans. If I don’t follow through on my promise, then I will probably have ended up wasting another person’s time.
I do these things, partly to “lead by example”, partly because I believe it’s just plain, decent respect, and partly because when I repeatedly deliver on my promises, I gain another’s trust in me.
On the other hand, if you can’t commit to something, then why not say that upfront? I believe that’s better than creating the expectation that you will live up to your word and then failing to do so.