Several years ago now Vincent Baker wrote this description of RPG resolution systems. He was mainly wanting to work out what (in his view) had gone wrong with his design of the game In a Wicked Age. But the method of analysis can be applied to other RPGs too. (Eg it was brought into a discussion of 4e five-and-a-half years ago).
Here's the explanation for the picture, and then the picture itself:
I'm interested in step 4: if the to hit roll succeeds, then - in the fiction - the attacking character hit the defending character. Is that right for D&D?
In the original DMG (p 61), Gygax says that
This suggests that, until the last few hp are worn away, a successful hit is really "cube-to-cube", like marking down reduced hp on a character sheet (step 5 in the diagram) - a mechanical thing, but not necessarily generating any particular "cloud" - any particular thing in the fiction.
In 4e, this sense that there is no particular connection between a successful hit and some definite thing in the fiction ("Agh! I'm hit!") is reinforced by the presence of inspirational/martial healing. In 5e, it is not quite so strongly reinforced as in 4e, but there is the fighter's Second Wind, the rather rapid healing default, and the discussion of hp loss (Basic PDF, sidebar on p 75): "When your current hit point total is half or more of your hit point maximum, you typically show no signs of injury."
So how is the resolution of D&D combat linked to the fiction of the game? Or is it all just cube-to-cube - no different from boardgaming, really - until the last blow is struck and the hp reach zero and now we know what is happening in the fiction?
4e answered this by layering lots of conditions onto its attacks - so the hp loss is boxes to boxes, but the forced movement or the infliction of some condition anchors each episode of resolution to the fiction in some fashion.
What about 5e?
(Hit points as meat is one answer, but a bit at odds with the p 75 sidebar. I guess I'm more interested in other answers.)
Here's the explanation for the picture, and then the picture itself:
The cloud means the game's fictional stuff; the cubes mean its real-world stuff. If you can point to it on the table, pick it up and hand it to someone, erase it from a character sheet, it goes in the cubes. If you can't, if it exists only in your imagination and conversation, it goes in the cloud.

I'm interested in step 4: if the to hit roll succeeds, then - in the fiction - the attacking character hit the defending character. Is that right for D&D?
In the original DMG (p 61), Gygax says that
It is not in the best interests of an adventure game . . . to delve too deeply into cut and thrust, parry and riposte. The location of a hit or wound, the sort of damage done, sprains, breaks, and dislocations are not the stuff of heroic fantasy. The reasons for this are manifold.
As has been detailed, hit points are not actually a measure of physical damage, by and large, as far as characters (and some other creatures as well) are concerned. Therefore, the location of hits and the type of damage caused are not germane to them. . . .
Envision, if you will, a fencing, boxing, or karate match. During the course of one minute of such competition there are numerous attacks which are unsuccessful, feints, maneuvering, and so forth. During a one minute melee round many attacks are made, but some are mere feints, while some are blocked or parried. One, or possibly several, have the chance to actually score damage. For such chances, the dice are rolled, and if the"to hit" number is equalled or exceeded, the attack was successful, but otherwise it too was avoided, blocked, parried, or whatever. Damage scored to characters or certain monsters is actually not substantially physical - a mere nick or scratch until the lost handful of hit points are considered - it is a matter of wearing away the endurance, the luck, the magical protections. . . .
Because of the relatively long period of time represented by the round, dexterity (dexterity, agility, speed, quickness) is represented by a more favorable armor class rating rather than as a factor in which opponent strikes the first blow. . . . The system of AD&D combat maximizes the sense of hand-to-hand combat and the life-and-death character of melee without undue complication.
As has been detailed, hit points are not actually a measure of physical damage, by and large, as far as characters (and some other creatures as well) are concerned. Therefore, the location of hits and the type of damage caused are not germane to them. . . .
Envision, if you will, a fencing, boxing, or karate match. During the course of one minute of such competition there are numerous attacks which are unsuccessful, feints, maneuvering, and so forth. During a one minute melee round many attacks are made, but some are mere feints, while some are blocked or parried. One, or possibly several, have the chance to actually score damage. For such chances, the dice are rolled, and if the"to hit" number is equalled or exceeded, the attack was successful, but otherwise it too was avoided, blocked, parried, or whatever. Damage scored to characters or certain monsters is actually not substantially physical - a mere nick or scratch until the lost handful of hit points are considered - it is a matter of wearing away the endurance, the luck, the magical protections. . . .
Because of the relatively long period of time represented by the round, dexterity (dexterity, agility, speed, quickness) is represented by a more favorable armor class rating rather than as a factor in which opponent strikes the first blow. . . . The system of AD&D combat maximizes the sense of hand-to-hand combat and the life-and-death character of melee without undue complication.
This suggests that, until the last few hp are worn away, a successful hit is really "cube-to-cube", like marking down reduced hp on a character sheet (step 5 in the diagram) - a mechanical thing, but not necessarily generating any particular "cloud" - any particular thing in the fiction.
In 4e, this sense that there is no particular connection between a successful hit and some definite thing in the fiction ("Agh! I'm hit!") is reinforced by the presence of inspirational/martial healing. In 5e, it is not quite so strongly reinforced as in 4e, but there is the fighter's Second Wind, the rather rapid healing default, and the discussion of hp loss (Basic PDF, sidebar on p 75): "When your current hit point total is half or more of your hit point maximum, you typically show no signs of injury."
So how is the resolution of D&D combat linked to the fiction of the game? Or is it all just cube-to-cube - no different from boardgaming, really - until the last blow is struck and the hp reach zero and now we know what is happening in the fiction?
4e answered this by layering lots of conditions onto its attacks - so the hp loss is boxes to boxes, but the forced movement or the infliction of some condition anchors each episode of resolution to the fiction in some fashion.
What about 5e?
(Hit points as meat is one answer, but a bit at odds with the p 75 sidebar. I guess I'm more interested in other answers.)