Overpromising

In The Art of Manliness I've read the following and instantly felt bad about the emails I've not responded and words I've not kept.

"No quality today can more readily set you apart from your peers than reliability. Doing the follow-through just mentioned. Showing up on time (and just plain showing up). Meeting deadlines. Managing expectations and not overpromising. Promptly responding to emails. Keeping your word."

I would like to be more reliable. My recent blunders with the project I'm working on is actually a sign that I've bit more than I could chew.

So the only question is actually not reliability. It's also in which work are you reliable? I'm in a highly demanding, original work that requires overpromising. They say it research and as Einstein put once, if we'd know what we're doing, we wouldn't call it research.

The subject matter of the work should also be considered. In some cases, we are forced to overpromise. We don't solve problems in research and development twice. They are always new problems and past success does not guarantee anything.

I understand what kind of business the article talks but there is also a reason why Google never gives a deadline for their services.