SPOILER : This guide is meant strictly for people who don't understand character development, veteran RPers will find little use for it.
For those who don't know me, my name is Yusuf Metwally (Yes I had a character that had my name.) and I have been dabbling around with the concept of character development for quite a while now.
I have been doing RP for over 6 years now (And I'm not a pro before anyone mentions it, I'm average at best) and the only thing I have managed to do properly is create a defined role/mindset for my character and never break it even if it will lose me some RP.
So, let's begin.
I have divided this guide into two segments.
1st : What is character development?
2nd : Why is it so important?
I'll answer both of these questions together at the same time.
So, character development is basically the way your character evolves from where they start all the way up till they die/leave/etc. and the main reason people do it is because it limits their RP to something dense and relatable rather than having it being sporadic and, honestly, unrealistic.
For example, a legal character would never break the law unless there's a very valid reason (Such as saving someone)
However, there are definite exceptions to this, as you can start as a very idealistic character and end up becoming a serial killer. (See Scumpy's Seth Rodgers for a great example of that.)
And that's the magic of character development, it lets you basically choose your own path, yet it also allows everything you do to be realistic and understandable as long as you RP everything properly.
Now, the thing about char dev. is that it requires actual understanding of how people interact with eachother, and it forces you to understand that you won't always win RP, in fact more often than not you'll be getting yourself in situations that you would never put yourself through on another character just because the character you're using has a specific mind-set and understanding that you cannot break.
Planning your character development is core for what you want to do, because you cannot just start a new character for the sake of having it and then keep it around.
Everything you do matters from naming your character all the way to how they interact.
Let's put it this way, imagine yourself playing let's say Skyrim or whatever, your attributes increase as you hone them, and the "class" you have is based on what you have actually done and which skills you took over the others.
Character development is exactly like that without the random numbers, the perks, and the skills.
Why? Because the only defining factor of how your character should be is you, so abide by your own laws!
Now the power of character development is great enough to the point where you can, quite literally, ignore RPing fear if you are RPing a suicidal person who doesn't care if they die, or you can talk your way out of every single situation if your character has a silver-tongue, or punch your way if your character is supposed to be very strong. It all comes down to what you do.
Big warning, though, do not make a superman because no one has no flaws.
Everyone is guilty of making a sporadically superman character at one point, I won't lie, I did it as well.
The problem with these characters is that they more often than not rely on their PG to win any situation.
Backstories, for example, allow you to be god-tier killer on a level one character, who cares?
It's not like it's against the rules to do something like that is it? No, it actually isn't, but it's terrible RP that you should avoid at all costs because it marks you as an idiot.
Furthermore, the less backstory you have, the better. (You should to use as a guideline but not like a fully-fleshed out char story, just have something that dictates the background of your character and that's it) ((Spoiler : I'm honestly super guilty of never following that rule because I like writing novels/short stories even if in my head)
Why? Because it gives you enough space to adapt your character to whatever RP you're doing.
You can go for joining the Sheriff's office with a super insecure character, it works, trust me. (See Arky's "On the verge of collapse" for further reference) or you can do complete prison RP (See the Nazi Lowriders character story) or you can even do basic citizen RP where you just get a minimum wage job and try to live your life. It's honestly your choice what you want to do and how you want to do it, that's the magic of char dev. It's limitless as long as you're doing it properly.
So, to conclude. Character development is important for your RP to be realistic and complete, because without it your RP seems random and lacking.
But character development is also great as it allows you to basically do whatever you want however you want it as long as you're doing it properly.
Hope this helped.