Sade Sati is the period during which Saturn transits three consecutive signs: the one before your Moon sign, your Moon sign itself, and the one after. Saturn takes about two and a half years per sign, so the whole passage lasts about seven and a half years — sade sati means "seven and a half".
It follows from arithmetic, not from anything about you. Saturn orbits in about 29.5 years, so every Moon sign receives a Sade Sati roughly every 29.5 years. Everyone gets one. Someone who lives to eighty will have had two complete ones and be partway through a third. There is no chart in which it does not happen and no way to avoid it.
Traditionally the three phases are read differently — the first as pressure building, the middle as the heaviest, the third as easing — and the classical descriptions emphasise delay, responsibility and the removal of things that were not load-bearing.
Two things are worth stating plainly. First, because the timing is public and calculable from a birth date alone, Sade Sati is the single most commercially exploited period in Indian astrology: it is the standard pretext for selling remedial services, and a person told they are entering it is a person with a predictable seven-and-a-half-year window of anxiety. Second, a period that happens to every human being roughly three times a lifetime cannot explain why a particular difficulty befell a particular person, because it was equally in progress for hundreds of millions of others who were fine.