Mistakes/carelessness in numbers is an absolute show-stopper in reality (and it also becomes a red flag in interview situations as well).
Let me explain why. Whenever I am the partner on a project, I need to be 100% sure and confident that the numbers are correct. I don't have the time nor the motivation to double-check details of my project team's work.
And it's really embarassing (in a trust-based relationship-business like consulting) if you base your recommendation and take-aways on wrong data, and it's even more embarassing if it would have been logically correct but just unnecessary carelessness about the numbers led to that situation.
You might get away with that once, maybe twice. Third time one of us will leave the organization, and I believe it's not me ;-)
Take-away: not only double-check, even triple-check your numbers - especially if you know already you are prone to such mistakes (and even if it's already 3am after a long day), and always do a sanity check to see if the numbers somehow are in a range of what you reasonably expected.
And make sure you never ever get a connotation about being sloppy with numbers - nobody will want to have you on his team.
Hope this helps - if so, please be so kind and give it a thumbs-up with the green upvote button below!