After 30-some years in the field, here are my observations:
If it works absolutely perfect in pre-prod, there's a 50% chance it'll fail in prod. Half the time there's a variable unaccounted for.
If it works well in pre-prod but I have a doubt, there's a 90% chance it'll fail in prod. If it doesn't fail right away, it'll fail when you least expect it.
Similarly, if it works, but I don't understand why it does, it'll break when I least expect it. Never leave working code alone if you don't understand it.
If it works OK in pre-prod, but performance could be better, it'll fail miserably in prod. Optimize in pre-prod, test the optimizations in prod.
A minor non-breaking bug in pre-prod becomes a major breaking bug in prod.
If it works absolutely perfect in pre-prod, there's a 50% chance it'll fail in prod. Half the time there's a variable unaccounted for.
If it works well in pre-prod but I have a doubt, there's a 90% chance it'll fail in prod. If it doesn't fail right away, it'll fail when you least expect it.
Similarly, if it works, but I don't understand why it does, it'll break when I least expect it. Never leave working code alone if you don't understand it.
If it works OK in pre-prod, but performance could be better, it'll fail miserably in prod. Optimize in pre-prod, test the optimizations in prod.
A minor non-breaking bug in pre-prod becomes a major breaking bug in prod.
If it works in prod and not in pre-prod, sync.
If it works in pre-prod and not in prod, worry.
Edited for formatting