The most important thing in your career (no matter what your career may be) is reliability.
You may have most impressive knowledge, you may have the ability to solve any problem you want, you may be the best salesperson, you may write the best and clearest project specifications, you may have the best insight into the market, you may even be all of that together, but if we can’t rely on you to do your work, if we can’t rely on you to show up, all of it is worth nothing.
Deliver what you’ve promised you would. And never promise something you can’t deliver. Reliable people are often worth a lot more than smart and talented people.