I say it's a very big topic because a lot of traders average out (spread out) their exits, but they don't really average their entries to that same extent, so their entry is mostly one-dimensional.
And why is that? Just because it gets a bit uncomfortable managing a position from the red side?

"Oh noes, I didn't get my flat stake entry spot on and I've made a bit of a loss because my trade didn't instantly run into profit. Ah well, I guess I'm supposed to automatically accept this loss now, like a good trader is supposed to."

Is it as clear-cut like that or is there more to it?
I feel it's hard to be so defensive with entries when the market itself is so aggressive, so for me it makes more sense to be more aggressive. I've seen even complete newbies manage their exits like a pro, almost on autopilot because they've seen others do it so many times in videos, so it's obviously not difficult to manage your position when it goes well from the start, but I think what makes or breaks a trader is how well he manages his losses and less than ideal entries etc.
I think the reason why people talk about "doubling up" and martingale is because a lot of people use flat staking, so as soon as you add the second stake you basically already "doubled up" on your trade and it feels like you're chasing losses etc, that's what I mean when I say position management becomes one-dimensional and you're forcing yourself or the market to be either right or wrong, without much middle ground. When in reality most of my actual trading is composed of middle ground stuff, for the most part I average out my results whether I'm right or wrong, if that makes sense

I for example like to be more flexible and stake only according to my confidence, which depending on what I'm trying to do usually means I spread out my initial entries with smaller stakes and then manage the position size from there accordingly, so I regularly add to the position whether it's going in profit or loss, for as long as I feel I'm taking decent valuable prices. Depending on price range I may spread out the entries every 2 or 3 ticks, and sometimes I read it wrong and the market ends up endlessly pushing against me but I'm usually often within scratching distance anyway because I keep adding and taking stakes out and buying myself a tick or two space etc. On the rare occasion that the market is completely one-dimensional with its fillrate and I'm unable to get anything matched on the other side, then I either have to start taking some losses or sit on it for a while if it's temporary and evaluate.
It's obviously not an exact science and sometimes I get pushed a bit more into loss, but usually doesn't take much at all for my position to start looking healthy again, and the upside can be pretty good from that point on as you can imagine. I confess that I am a bit lazy with my entries and like to get involved as soon as possible without patiently waiting for good entries, which means I sometimes play the averaging game.
In other words, I arrive at a market and do a rough evaluation of the ranges and then just try to get matched at what I consider good prices, and while I wait for bigger swings of price to come (if they even come) I try to make the most of the market noise by adding more ticks to my position from scalps and such, so the odds are always stacked in my favor, so to speak.