When you invest the same rupee amount every month through a SIP, your money buys a varying number of units depending on the price that month. In a dip, ₹5,000 buys more units; in a rally, it buys fewer.
Over time this averages out your purchase price and removes the temptation to time the market. You never invest everything at a peak, and you keep buying steadily through downturns when others panic.
For example, if a fund's price swings between ₹40 and ₹60, a fixed monthly investment ends up with an average cost below the simple midpoint, because more units were bought at the lower price. It is one of the quiet advantages of disciplined, regular investing.