The basic idea behind SIP is that while the general direction of an equity investment is upwards, it is not possible to reliably predict the actual fluctuations that it may undergo as part of its general trend. Instead of trying to time one's investments, one should regularly invest a constant amount. As time goes by and the investment's NAV or market price fluctuates, this will automatically ensure that when the price was low, you ended up purchasing a larger number of shares or units. Eventually, when you want to redeem your investment, all the units are worth the same price. However, because your SIP meant that you bought a larger number of units whenever the price was low, your returns are higher than they would have been otherwise.

That's the way it should work. However, you have to allow it to work by going on investing when the market is low and not try to time it. At one level, SIPs are nothing more than a psychological trick to make you invest when the market is low without having to guess what it will do next.