It’s important to have ETA, not just because someone else wants to coordinate with you. But it’s important for self introspection, self assessing, it’s important for one to know what all are the puzzle blocks in the problem. I remember a quote
A problem well put is half solved.
So ETA is thinking about the problem. ETA is not to impress anyone with your skills especially in software development, otherwise you would be fighting the bugs rest of the time. Some times there is pressure of determining the correct ETA, don’t give ETA for whole problem, break the into chunks and give ETA for individual chunks.
Think ETA as assembling the Rubik’s cube. It may seem messy initially, but step by step it will be solved. Solve the first layer, then second layer and lastly the third layer.
Also ETA is no excuse to comprise on quality, a half baked product to match ETA is no worth.
*ETA = Estimated time of arrival