I have seen that markets rarely trade at fair value. They trade either way a premium or at a discount. For eg., If you think that Index's fair value is 15,000, it can go well below 10,000 for God knows why and if you think 20,000 is a fair value, it can go well beyond 25,000 before you see corrections. So, stop averaging by fresh money ay every fall and stop booking profits at every rise. Stop guessing the true value of index and stocks. Stay invested for long term and markets will ultimately reward you.