How ah? When go up let go or when go down let go?
Other people buy low sell High.
But due to SG kiasu kiasi culture, Sinkies always end up Buy High Sell Low when stocks go down slightly.
When it comes to long-term investment, buying stock should be about investing in a company after doing all the due diligence with confidence that the company stock will go up in the long run, typically 6 months or more so that it becomes an appreciating asset.
You should only sell the stock when:
1) You researched and know that the stock has likely reached it's peak or nearing its peak, then its time to harvest for maximum capital gains.
2) You read about something drastic and bad going to happen to the company, e.g. CEO up lorry, quarter earnings drop drastically and the stock is likely going to plunge like no tomorrow. Then it's time to sell at lower profit or cut losses.
But in reality, it's easier said than done as your info is always lagging behind institutional investors who are like sharks pwning retail investors all the time with many deceptive false signals. End of the day, it's up to your own skillset and business acumen. Nobody can teach you on this, you have to go thru the ritual.