"The project is late and over budget because our estimates were overly optimistic."
"We were overly optimistic in our estimates, and as a result the project is taking longer and costing more that initially expected."
The difference is probably coming across as more subtle that it is because you have the two sentences right next to each other. Consider, though, that the emphasis of each statement is on the first part.
In the first scenario you are saying that the project is late and explaining (or justifying) why. In the second scenario you are advising that your estmates were optimistic and explaining the consequences.
The way you speak affects the way I interpret what you say, and consequently, the way I feel about you and your work.
Picture by mynameisharsha cc @ Flickr