You'll see it in all the parenting magazines, one of the most important aspects of discipline is consistency. If you say you will do something, you have to do it. The same for reward: don't promise something unless you're 100% sure you can deliver. 

Consistency brings a sense of stability and trust. Consistency over long periods of time develops character as well. If you want to be a trusted employee, a prized student, or a respected artist, be consistent.  

Show that you can deliver over and over again, and people will seek you out. But no one is perfect, and when there is a responsibility you can't keep, be open and notify people as quickly as possible. That kind of transparency, shown consistently, is just as valuable.