You don't have to promise and not fulfill. It is better you just surprise someone instead of promising and not fulfill because you are keeping the person in a very big expectation but it's not always okay.
The promise must be fulfilled when made always. It's just like when you make a promise just like you're dealing with God. God does not want us to take a vow that we are not prepared to fulfill.
The bible tells us that God have no pleasure in fools, whenever we make a bow, we must try to fulfill it. When we make a vow and not pay, it is a sin. To make a vow not pay is such a big crime, it's better if you just make give according to your hearts, or according to your please then making a vow that you know you cannot fulfill.
Whenever we are caught in a situation where we are making a promise and not feeling it we are not doing the right thing, We are really costing someone to see but you see when desire comments is like a tree of life. We must be willing to make a promise and also fulfill it at the right time.