Question: If the Ascendant is more important than the Moon or the Sun in a horoscope, then why does Dasha begin with the planetary lord of the nakshatra the Moon is placed in? Why not the planetary lord of the nakshatra the Ascendant is placed in?
The president is more important than the joint-chief-of-staff but this doesn’t mean that the join-chief will have no duties and the president will do everything. Similarly the ascendant is more important than the Moon, but this doesn’t mean the Moon has no importance and no role to play.
Of all the planets, Moon is most related to rhythm and timing – she shows the most granularity of rhythm by changing her position, size, etc. dramatically day by day. Daśā’s are about the rhythm and timing of the horoscope’s effects, therefore the Moon’s nakṣatra (constellation) determines the daśā schedule.
Another reason is specific to the daśā systems that are sidereal (nakṣatra based). Most of the daśā systems are, and the most widely used viṁśottarī daśā is. The reason is that nakṣatras are stars, and stars come out at night, and thus relate primarily to the Moon. The Moon is the most important astrological factor in relation to the 27 sidereal constellations (nakṣatra). The ascendant is a tropical factor (the position of the eastern horizon), not a stellar factor, therefore it would be less appropriate to use it for determining an inherently sidereal calculation.