Every culture has its own way of dealing with death, and exactly how they do it often comes down to that culture's views on the afterlife. Or in some cultures' cases, "before-life." Here in the West, we might see other cultures' funerary practices as morbid or unthinkable. But they might well say the same of us. That sort of cultural relativism does apply to most practices. Except for that one we always have a problem wrapping our minds around: human sacrifice.
The custom of sati, a widow killing herself following a husband's death, seems fairly barbaric in some ways. Prehistoric, almost. And it is, on both counts. But is this really so different from what we see in something like Romeo and Juliet? Two people deeply in love, entering the hereafter together?
Depending on your age and views of the afterlife (or in India's case, reincarnation), the idea of Sati may be either very easy or very difficult to understand. But there is some beauty to be found in the notion. Just ask Juliet.
Sati has long been associated with India, primarily on the basis that it was the last place commonly or visibly practiced. But India was hardly the first or only culture to engage in this sort of ritual. You can find instances of widow sacrifice all the way from Korea through Norse Viking country, down to Mesoamerican Aztecs and Incans. Some say it's still practiced quietly in China and Vietnam — though in truth, you won't find many corners of the world where widow suicide doesn't happen on a somewhat regular basis.
Still, not quite as regular as public burnings were in India at one point. It's estimated that at the peak of sati's popularity in the 15th-18th centuries, several thousand widows a year burned themselves on their husbands funeral pyres.
The iconic image of sati is that of a woman climbing onto her husband's funeral pyre or being set afire with it. Certainly, this did happen, at least as recently as the 18th century. However, a woman could also choose a less painful method, and be placed on the pyre or buried with her husband afterward. Poison or drug overdose was often the first choice, though in some cases they would administer just enough to make the woman comatose. She would be "burned alive," but not while awake. Other times, she might opt for a snakebite or a blade to the wrists or throat before burning.
There have always been rules surrounding sati and who could commit it. Women with young children to care for, or who were pregnant or menstruating, couldn't commit ritual suicide. This was seen as sacrificing the life of the child along with her own. Though again, there are some practical considerations here — not least of which being that a woman capable of bearing children may wish to re-marry at some point.
At no point, all the way up until death itself, was a woman absolutely committed to sati. Women who did commit it were said to have died virtuous and chaste, which is big deal in Hindu culture. A woman who dies chaste dies has much better karma and has a better chance of being re-born into a better life in the next cycle. Perhaps, even with her husband.
This might be another part of the justification for Brahmin women—women of a higher caste—not committing sati. As Brahmin, they were already of the highest caste possible and stood to benefit nothing karmically from sati. In any case, any woman could opt out of sati at any point. Custom demanded that a male relative remain near her funeral pyre to pull her out, should she change her mind at the last possible moment.