Male channelers in The Wheel of Time’s world can’t use the One Power without eventually losing their minds. Women, on the other hand, can safely tap into the True Source. It’s for this reason that Aes Sedai membership is limited only to women, who don’t have to worry about the possibility of insanity.
It was established early on in Amazon’s Wheel of Time show that though the majority of the One Power channelers that exist in the world are female, there are some men out there who can touch the True Source. The problem is that they’re doomed to go insane. The “madness” that goes with being a male channeler was on display when Logain was seen speaking to the “voices” he believed were the previous incarnations of the Dragon. After the Wheel of Time season 1 finale, Rand (Josha Stradowksi) now fears that the same fate will befall him. The knowledge that he, like the Dragon before him, will be cursed with madness has caused him to take his leave of Moiraine’s group.
The One Power not being safe for men in Wheel of Time can be attributed to the actions of the Dark One and how the True Source is divided. The One Power consists of two halves, saidin and saidar. Saidin is what men use when they access the Source, whereas women draw upon saidar. Thousands of years ago, saidin was tainted by the Dark One’s touch. In corrupting saidin, the Dark One ensured that anyone who uses the male half of the One Power will lose their sanity. Thom (Alexandre Willaume) mentioned this to Rand in Wheel of Time episode 4.
What the Dark One did to the One Power all those years ago is ultimately what set in motion the fall of Lews Therin Telamon (the last Dragon) and the Breaking of the World. Lews Therin had an army of 99 male Aes Sedai, but lost them all to the tainting of saidin, which drove them insane. So while the Dragon receives much of the blame for the destruction that was wrought during the War of the Shadow, it was really the Dark One who made it all possible.
Even now, the Dark One’s taint on the True Source lingers. For Wheel of Time’s villains, the problems with saidin are good for their cause. Since male channelers like Logain are typically more powerful than the female Aes Sedai, they could be formidable allies in their efforts to overcome the Dark One’s forces. Instead, they’re hunted down and gentled by members of the Red Ajah. Most, like Thom’s nephew, don’t survive for long after enduring the process. In The Wheel of Time’s world, men who have the One Power have tragic, troubled futures ahead of them.