When I just started out as a junior analyst at McKinsey I always wondered how my project manager was able to spot a mistake or inconsistency in my slides in a second. I had been working on this all night (sometimes literally), build all the spreadsheets, mastered all the detail, and in she comes and says after a few seconds: “that number looks wrong to me”, and yes, there was a bug in my analysis.
The secret is take some distance from your work. Look through the slides without connecting them to your Excel sheet. Sales numbers on page 3, should be the same as sales numbers on page 16. A soft drink can is unlikely to cost $50. Simple checks and a cool head.
If you do not check your slides, your manager, or your client will for sure.