The easy answer is to how you become a Sith (apart from already having the ability to use the force) is you get angry or “give in to the hate.”
Exactly how and why you might give into the hate has a slightly surprising cause that you might not be aware of and might make more people Sith than Jedi.
The purchase of the Star Wars franchise by Disney has had the unexpected consequence of channeling the Disney agenda into the representation of Jedi and Sith. In particular, the Disney agenda makes it likely that more people will be turned to the dark side than remain Jedi.
Disney is well known for an antagonist representation of parents. How many movies start with a parent (more frequently a mother) getting killed or already being dead? More than I’m bothered to count.
As the continuing franchise exposes us to more and more force welding characters, a trend begins to appear and is linked to families. The original trilogy introduced Jedi without any mention of Sith. Darth Vader and the Emperor are merely Imperial and on the dark side. The prequel trilogy gave us an interesting insight into becoming a Jedi. Initially, Qui-Gon Jinn isn’t happy about taking on Anakin Skywalker because he is too old. We are introduced to the idea that the Jedi recruit children, removing them from their families and training them in the way of the force. This reinforces the idea of Jedi as a monastic order who are not allowed attachments or possessions. They are also not allowed to marry because it leads to the dark side. Therein lies the interesting element that is more likely to make you Sith than Jedi.
Have your parents or children ever annoyed you? It’s a rhetorical question. Of course they have. Looking at Jedi who have turned to the dark side you will find parents and children running around making the force wielding individuals so angry they just have to give in to the anger.
Anakin Skywalker has a mother who is killed by Sand People. He also has kids. Kylo Ren has parents and ends up the product of a broken home. Emperor Palpatine has a child who run off with his grandkid. Nothing is more likely to piss someone off than kids that can’t listen and won’t let you see your grandkids.
Rey is dropped off by her parents who then get killed meaning she just about makes it. Luke only has a sister and a nephew (not counting his aunt and uncle who die horrible deaths) and he has to live on a deserted island so he doesn’t turn into a dark side rage machine. Leia lays down the lightsaber before she becomes a Jedi because she knows. All the rest of the Jedis live in isolated locations (Yoda and Obi-Wan Kenobi) or are the product of the monastic isolation of kids from their families. Even Baby Yoda is devoid of parents being carted around by the Mandalorian and emotionless guardian rather than a parent.
Disney didn’t start the trend, but the last three Star Wars films have certainly compacted the trend and leads to a unanimous conclusion, if you are Jedi, ditch the parents and don’t even think about kids because they are send you straight to the dark side. And what can you hope for then? A last minute moment of redemption just before you die after you have slaughtered countless people. Yeah, I can completely see how parents and kids can do that to you.
May the force be with someone else because I’m not sure I want it.