What are some useful tips in being able to scope/size/determine how long a User Story will take to complete?

Hi,

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I am a junior developer at my company and i’m kind of struggling with this.

Issues come up, blockers come up, and or something I wasn’t aware of comes up and sometimes I am not able to deliver a story on time, especially if it’s a really large story.

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I have gotten fairly good at breaking down tasks, but understanding the scope at times is difficult for me.

Are there any questions I should be asking myself/leads/product team, etc?

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Any advice would help!

I dislike not being able to fully size things and my manager makes me feel bad about it. He doesn’t understand that I lack wisdom in a lot of areas and I’m still a new engineer. He cannot code and he doesn’t have an engineering background. He’s a project manager who some how ended up in a dev manager role through his buddy (who is the director), which has now earned me an unfavorable spot due to lack of knowledge on my half and lack of capability on my manager’s side which just ends up with me being thrown under the bus.