@DRDMovieMusings said:

SPOILERS - you've been warned - if you haven't seen this movie and wish to, stop reading now, watch it, then come back to discuss.

Ken Mattingly was on the flight crew but couldn't go because he got sick. Imagine the disappointment! The opportunity of a lifetime, the crowning achievement of an astronaut's career, dashed. Heartbreaking, right? Life's not fair!

Turns out, a critical catastrophe scuttled any chances of landing on the moon and threatened the very lives of his friends.

To create a solution required to power up the command module from a full shutdown, the ground crew needed someone on the team with a particular expertise, and the person with that expertise was Ken Mattingly.

Had he been up there with them, that team might not have been able to devise the approach, and they'd likely have died. What, at first, was a terrific disappointment was eventually revealed to be the best thing that could happen, under the circumstances, it just took some time for that reversal of perception to emerge.

And that's how life works, sometimes. Ancient wisdom literature that's thousands of years old illustrated this idea, and its modern application, far removed from the original scenario, celebrates the timelessness of truth.

According to this article in the Smithsonian magazine, Howard exaggerated Mattingly's role in the reentry drama.

"On the tenth anniversary DVD of Apollo 13, Lovell and his wife Marilyn detail several inaccuracies, including the inflated role of astronaut Ken Mattingly (whose work is an amalgamation of efforts undertaken by several astronauts and engineers), exaggerated doubts about Swigert's role in the mission, and the fact that the engine burn that corrected their course was not, as the movie showed, aimed in the direction of Earth."

https://www.smithsonianmag.com/air-space-magazine/did-ron-howard-exaggerate-the-reentry-scene-in-the-movie-apollo-13-17639496/