However, there will be times when a trout just follows, almost takes, or comes and goes only to come again. Holding back in such situations comes with experience.
Jim, I've noticed that there seem to be certain times of year when the fish don't slam flies as much as usual. They sip them very purposefully, and this is the time that the ability to hold back on the hook set is really crucial. In the spring when the "big" hatches are on, fish (other than the multitude of dinks) will rise leisurely to the buffet above. Same thing happens in the fall, especially when the olives are on the water. Low clear water seems to be a recipe for the much better inspection on a rise you described so well above. The key in those situations is to wait until the fish has taken the fly and started to turn its head before setting. If you set too fast it will pull the fly straight out of the fishes mouth...
"Then He said to them, 'Follow Me, and I will make you fishers of men.'" Matthew 4:19