This! It's more or less impossible to correctly estimate how long it will take to develop anything but the most basic pieces of software, and even then you can't be sure.
I've had so managers who just don't get that there are so many unknown variables in the software development process.
No matter what estimate you give, you cannot win. Estimate short, but it takes longer? Then you are accused of not knowing what you're doing. Estimate long, but come in short? Then you are expected to shorten all future estimates. Estimate right? Nah, that never happens.
Every price of software developed is different and will take a different amount of time to be developed. It is really quite stressful for a dev who is working their ass off to hit difficult targets in an organisation that refuses to be flexible about that sort of stuff.