When we say we can’t do something, we can cause some short term disappointment and frustration. However, when we say we will do something and then regularly delay delivering and make excuse, disappointment and frustration is prolonged and grows.
Being up front about delays or capacity may be uncomfortable but it makes life easier for everyone on your team. Straightforward communication allows others to plan and get on with their work. Time is not wasted in disappointment.
The choice is up to us.