Getting something right the first time is hard, if not impossible. So why is it that I so rarely hear about homebrewers repeating beers? Multiple surveys indicate that homebrewers brew an average of once per month, and I don't have much evidence (anecdotal or otherwise) that homebrewers are producing the same recipe twice in a row.
I sincerely think that's a mistake, particularly for newer brewers, but also for those with more batches through their mash tun. The only way to know - know - that you're making what you intend to make is to repeat your process and get the same result.
Process is King
I don't think I know a single good-to-great brewer that doesn't pay close attention to their process. There's a good reason for that. It isn't that carefree, devil-may-care brewers can't make incredible beer, it's that hitting your target requires two steps to be performed consistently: aiming and pulling the trigger. These generate validity and reliability in your brewing.
Validity is the extent to which there's correspondence between what you think you're aiming at and what you're actually aiming at. If you're consistently looking down the sights in the same way, then you should get a much more valid result.
Reliability is simple, too - reliability is repeatability, and reliability depends absolutely on your commitment to doing the same thing in the same way every time.
Not all beer that's targeted validly and produced reliably is good beer - but if it isn't, it's a hell of a lot easier to bring it into line since you can rest easy knowing that the changes you introduce should, all else being equal, produce the anticipated changes.
So you think you have your process under control - now prove it. Make the same beer twice.
I don't mean "brew the same style from the same recipe twice," and I certainly don't mean "change every recipe to improve it with every brew day." I mean it literally. Brew the same beer, from the same recipe, on the same equipment and using the same process, with the goal of producing an identical beer.
Clone your own beer, effectively, and then you can claim to have your process under control. And lest you think, "well of COURSE they're going to be more-or-less identical!," I've seen this done lots of times and it almost never happens that way the first time.
Brewing is a pretty damned robust process. As we say, wort wants to become beer. But that doesn't mean that small inconsistencies in process won't cause large downstream effects. You'll get beer. You might even get outstanding beer. You won't get the same beer, though, without practice.
Don't Think - Know
When I bring this up among brewers, the answer I get most often is, "oh, I definitely brew the same way every time." When I ask how they know, they seem confused. "Well, I like all my beers, and they do well in competition, and..." Honestly, there's nothing wrong with that as an answer to the question "are you a good brewer?" But it's not much of an answer to the question "are you a consistent brewer with good control over recipe-building and process?"
The only way to know that is to do it. I know there's an impulse to brew, solicit feedback, and tweak with the goal of improvement. I also know that brewers often end up chasing their tails "improving" their beer before they have a good handle on their process - and know that they do. Instead, they're trying to fix their beer based on a "maybe" (as all such evaluations tend to be) in a process that is itself a "maybe." We can't remove the inherent subjectivity of the feedback and evaluation we get. We can, though, lock down the process end of the equation.
Once you cross that threshold, as validated by back-to-back brews, you can make adjustments confidently and effectively.
Keep it simple.