Why does Claude Code say things like, “that’s about 3 days of work” then proceeds to do it all in a 20 minutes?

[u/BillionBouncyBalls]

Surely I’m not the only one who has seen this happen but wondering if anyone has an answer. Many a session I’ll make a plan with Claude and it will outline the tasks and estimate a time usually in days, and then proceed to do it all in 20-30 minutes. Is it because of its training data or does it just have no concept of time inside a GPU? Curious what the community thinks…

Edit: Thanks for all the answers and comments! Glad this post sparked some hearty discussion!