All available signs indicate that Calvin Johnson’s NFL career is over. He’s borne a heavy burden for the Detroit Lions for nine seasons, during which he has performed at historically great levels, although injuries have limited his (still above-average) production in recent seasons. Nevertheless, outside of Johnson’s reportedly expressed desire to walk away from the game, there is nothing to suggest that, if he decided to continue his career, he would not continue to play at a very high level.

In fact, FiveThirtyEight’s projections show that if Johnson, who has compiled 11,619 receiving yards, stayed in the game, he could pull down an additional 4,355:

That would account for twenty-seven-percent of his projected total receiving yards, and if Johnson were to reach that projected total of 15,974 yards, he would finish as the number two all-time receiver, just ahead of Terrell Owens’ 15,934, though still well behind Jerry Rice’s absurd 22,895. (So long as we’re projecting, it’s worth noting, as the article does, that Larry Fitzgerald (17,323) and Brandon Marshall (16,323) both project to finish ahead of Johnson’s projected mark.)

These projections, like many sports projections, are based in significant part on the performance arcs of past players. This is a reasonable methodological approach, and it’s probably the best and most widely used for these purposes. It has a few blind spots that are worth keeping in mind, however. One of those is the health of the individual player. There is no doubt that today’s players take their health and well-being more seriously and with a broader perspective than those of previous generations, including Rice’s. (There always will be exceptions, of course.) The backward-looking orientation of these projections mean that they will miss both new (or effectively hidden) injuries to the specific player, as well as new general trends regarding health and wellness, both of which could limit Johnson’s future production. So too, of course, could his desire to stop playing entirely. Also not directly included are rule changes and general changes in strategy, and here, those– rules that favor passing offense and a strategic shift to emphasize passing in offensive schemes– actually could push Johnson’s actual future output above his projected total.

Still, Johnson is thirty years old, he’s been banged up in each of his last few seasons, and his team’s present trajectory fairly is categorized as stagnant. As the FiveThirtyEight article reasonably concluded, “if Johnson ultimately decides to leave, good for him. If he ultimately decides to stay, good for football.” For fans, sports always will, in relatively equal parts, be about what was and what could be, and, as fun and important as imagining and projecting the sports future is, it’s just as important to realize what we have and have had play out before our eyes. Luckily for us, Johnson made the latter very easy and very enjoyable.