@gweanakjakarta: No, you didn't get it wrong, just the cause. Artoria chose to seal off her emotions because she believed that to be required to become an "ideal king". To be fair, it worked as intended: She was perfectly impartial and just throughout her reign. It's just that her lack of emotion alienated her from her subjects, including many knights who served in her military, and probably was a factor in the rift that formed between her and Mordred that ultimately led to her refusing to make said child her heir, thus sparking the infamous rebellion that saw the kingdom that she had forged destroyed.
As Iskandar later tells her, she was a perfect ruler, but a shitty leader (and he, incidentally, is the opposite: a shitty ruler, but the best leader his people ever had by virtue of living his life to the fullest alongside them, i.e. acting as human as any of his subjects were).