If I can replicate a result, that's fairly straightforward: I replicated it!
If I can't, that doesn't mean the result was necessarily wrong; maybe I just messed up, or got unlucky and the result only happens 20% of the time. You might need several independent failed replications to start to be confident that the original result was definitely wrong.
It's like saying: there's a buried treasure in this acre. If I find it on my first pass through with a metal detector, job done. If I don't find it on my first pass, I'll probably need to make several more passes, maybe bring in fancier equipment and so on, before I could be pretty confident that it's not there.
Someone claims that a human can run a 5 minute mile.
To prove it true, you just need to show a human who can run that fast. To provide it fast, you have to accumulate incontrovertible evidence that it's simply beyond us...
