This. Absent tax issues, every day you own a stock is exactly the same as making a decision to buy a stock on that day at that day's price. There is no "hold;" There is only "buy" and "sell."
Now if I could only consistently follow my own advice.
A wise investor taught me this at an early age. Take each of your positions and apply this logic. While I've done pretty well over the years, I would have done much better had I been strict about following the policy. Instead I have fallen prey to emotion, the tail wagging the dog, and the fallacy of believing management.
1) Emotion - we are emotion driven creatures, and this clouds our investment decisions. It is on both fronts - the desire to keep something that has moved up, even while we know the future prospects don't warrant the price. This also applies to losers, not asking ourselves why we bought it (investment thesis) and if that thesis still applies. This also means questioning our assumptions - has something fundamentally changed that we are skimming over or ignoring that changes the thesis.
2) Tail wagging the dog - By this I mean tax consequences. This has bitten me several times, both in the desire not to sell a winner due to capital gains, and the desire to unload it because due to a loss. (A corollary issue that MANY investors have to NOT sell their losers but instead to double down or think that it will come back (see 3)).
3)Fallacy of believing management - I've had several occasions where I questioned the investment, but held on with the believe that management knew something that I didn't. The latest (for me) is that I was a long time owner of OXY (Occidental), with a smallish position that I bought way back in 2005 (and on which I had a profit). Then they (OXY) got into a bidding war for Anadarko Petroleum (which I questioned) and even worse did the private high priced deal with Buffet. Had I done what I thought (this looks like a dumb deal) and SOLD IT IMMEDIATELY, I would have walked away with a profit. But no, I held it thinking management knew something about those assets and ended up losing money because of this. In then end, CEO's of companies are in it for themselves, and it is best that we as small fish investors remember this. (Not the first time I've been burned). A long time ago I would go to the annual meetings to see CEO's in action, and made very wise decisions based on meeting/assessing the CEO (both positive and negative).
Discipline is key - and my biggest failings in investing have been lack of discipline.