Why did Stannis leave? He was going places — investigating? — with Jon Arryn before his death, and now Stannis has abandoned King’s Landing. Apparently he’s either too careful to succeed or he’s a coward. Also, he’s quite a prude and no one likes him. So there.
Seat Stannis on the throne and the realm will bleed.
My God, he’s bitter. He’s steeped in poison of his own thoughts. He’s a resentful person, envious of Renly. And Ned. Wow, is Stannis a horrible, small-minded tyrant. However, he’s not kind, he’s not successful, and he’s not witty. None of the Heart Types fit him.
One goes to Four in weakness. The WHAMming (What About Me?), the envy, are part of that slide. The obsession with rules and details are the One side. He’s petty and selfish, with none of the charm of either number. A turn toward Seven would be a strength move. You can see how if he considered his options — join with Renly, join with Winterfell — he would improve his chances. Instead he chooses the Red Woman, the occult, which narrows his odds even further. Why in the world did Ned consider this man a possible monarch? No bloodline is strong enough to make Stannis worthy.