If you're daytrading, I think the most important rule other than cutting your losses is taking your profits. A good profit that you let melt away because you wanted to hold for more is in my opinion more destabilizing emotionally than seeing a stock run 2 points higher after you sold for a .50 gain. Well either case is pretty infuriating, but at least in the second case you've come away with a gain on your trade, as well as the knowledge that you had the right idea in the bigger picture.
The funny thing is, the only times it seems I'm capable of being short a stock a few ticks off the day's high or being long right at the low is if I'm purely in scalp mode, and hence taking very small gains relative to the eventual move. Conversely, on the days that I'm actively looking for position trades to take, I usually find my entries are quite bad relative to the day's range. Mixing time frames is a difficult thing to do, and having seller's remorse is really a symptom of not being sure of which time frame you are most comfortable trading. If it really bugs you to see stocks make multi-point runs after you've exited, and want to change your time frame in effort to capture those kinds of moves, be prepared to see MANY of your future open profits go back to zero or worse; that just comes with the territory of the longer time frame.