1) Buying tips without doing your own homework. A friend, a WhatsApp group, or a YouTuber says 'this stock will 3x' — and you buy without reading a single quarterly report. This ends badly in ~80% of cases.
2) Selling in panic. The market falls 15%, headlines shout crisis, you sell to 'stop the bleeding'. Two years later the market is higher than where you sold. The average investor's return trails the market by 4–5% annually because of this exact pattern.
3) Position sizing far too big. You put 40% of your money into one stock because you're 'super convinced'. When it drops 50%, your entire portfolio drops 20% from one decision.
4) Chasing last year's winners. Whatever theme performed best last year is where beginners pile in this year — right at the top. Same story in 2018 (small-caps), 2020 (tech), 2022 (defense stocks).
5) Ignoring costs and taxes. Frequent trading generates STT, brokerage and short-term capital gains tax. Long-term (holding >1 year) equity gains beyond ₹1.25 lakh/year are taxed at just 12.5%; anything sold within a year is taxed at 20%. Long holds are also tax-efficient.