When should you sell a stock?

The market has been bullish these 2 weeks.

I would like to maximize my profits, sell at the peak (hopefully) and repurchase when the stock is low. However, to time the market is very difficult and I do not encourage that too.

But there are still some very valid reasons on when I sell my stock.

1. When it is very likely (i.e. beyond a reasonable doubt) that the stock is overvalued.

A P/E ratio that is ridiculously high or a very bullish stock that keeps going up within a short period(a few days) without any significant company news can indicate that the stock is being driven by speculators.

I monitor the stock market every hourly x8 hours x 5 days a week x 12 months a year, and so far it has been 1 yr 8 months. Really eat too free lol.

There was a time where Q&M irrationally shot up to $1.00 at its peak. The normal trading price was around $0.68-$0.72 over the year.

StarHub traded at its peak of $4.46 when the average over the year was about $4.05-$4.18 before the 4th Telco came in.

For one to see when your stock is overvalued, I think you would really have to know your own stock SO WELL until you know how it might behave according to STI's movements.

There are some technical movements and volatility (we call that 'Beta' in a stock) unique to each stock Some stocks have very high beta (Noble) whereas some stocks are forever so stagnant (Reits). You can only confidently sell your stock if you know it has suddenly behaved irrationally.

2. When its fundamentals have changed

 In 2015, the oil price started to spell trouble and that was a good time to sell oil stocks like Keppel when it was trading at $9+.

In 2015, the announcement of the 4th Telco came and there were already plans for its entry. That was a good time to say goodbye to Starhub and M1 :(

A shift of fundamentals include the overall industry outlook and the company's competitiveness.

3. When you know you have a better opportunity

I sold Capital mall trust when I earned some decent profits then and I believed that at that particular time, it has hit a high. I sold it off and bought Ascendas Reit when I honestly think it was undervalued (at that time).  This is a reason to sell a stock- to purchase a stock that is performing better (hopefully undervalued).

True enough, A-Reit hit a high about 2 months later and I sold it off again. I am still pessimistic about the market especially in the US side. I highly believe that US is heading for a recession this year.

Digress, I do need some funds for my war chest. I do not think that my opportunity cost to hold off a bit later will be that high.

Well, these are just my opinions learnt through several heart aches; I hope I am improving :)