Mass Effect 3 has different endings depending on your actions throughout the game. I'm not asking what actions affect this (which is described here) but rather Why does this happen?

(Obvious spoilers):

Depending upon your Readiness Rating and/or effective military strength, if you select "destroy the Reapers", it changes the result of using the Crucible. For example, Earth may be completely destroyed, partially devastated, or saved.

Why does the power of the forces you united to face the Reaper determine how this big destroying ray affects Earth? How can the fact that you have recruited some characters change the way the Crucible works?

[ Side Comment : Bioware made a horrible ending, they ruined the whole series, and blah blah blah... ]

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    This type of ending is not uncommon. The historical reason behind linking two seemingly unrelated things (the type of ending you get, with some measurable quantity) is to reward the player with a better ending depending on how well they performed toward some kind of goal, regardless of how that goal should actually affect the ending. For example, take Chrono Trigger for example (not a perfect example...), one of the early examples of "getting different endings" depending on how few allies you use to defeat the final boss affects how "good" (cool) your ending sequence is. Jun 21, 2012 at 16:50
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    Yeah but Chrono Trigger had something like 16 different endings, including one with the Game Designer in it. Let us not forget the FFX-2 travesty (and I'll sadly admit, busted my buns trying to get 100%. Futility... when now you can just watch a YouTube video and save yourself having suicidal thoughts making the attempt).
    – Jersey
    Sep 6, 2013 at 17:23

3 Answers 3


The Crucible is a piece of technology that was hauled through the middle of a huge space battle. As stated in the game, the Shield Fleet is part of the combined fleet held in reserve purely to escort and defend the Crucible. As the Sol system relay, the Charon Relay, is on the edge of the system, near Pluto, this leaves a not-insignificant amount of space to traverse to reach the Citadel in Earth's orbit.

Given these facts, it was my thought that the salvation or destruction of Earth was a product of the effectiveness of the Crucible after wading through the battle. Even if it was not engaged in the fight until it reached Earth's orbit, it is very clearly shown that the fighting is very intense. The fewer war assets you have available to you, the less effective the Shield fleet will be at defending the Crucible from attack. Also, depending on your war assets, the Sword fleet may start taking heavy losses, leading to less damage done to the Reaper fleet as the Crucible approached. Lastly, the Crucible-related war assets list a number of offensive and defensive technologies that show that the Crucible was built to participate in the fight. While I do not recall seeing the Crucible taking direct fire in any of the cut-scenes, it was not my impression that it reached the Citadel unscathed. Any damage done to the Crucible could have lead to malfunction(s) or errors in key systems that would otherwise have caused the beam to leave Earth unharmed.

That was my impression. I hope this helps.


I quote the above, and add that several crucible-related war assets are made of scientists. It may well mean that the more scientists you put on building the crucible, the better built it is, more reliable etc. As it is a new tech, too few scientists and skilled workers building it increase the risk that it backfires. Note what Adm. Hackett says about Rachni workers: "turned out they have a knack on weapons of mass destruction".


Sadly, while I totally agree with Zoneman's answer, and it makes sense on paper... really, BioWare? It's a weapon of massive destruction, I don't really think it cares that you've got more foot crunchies or not. I don't remember the Enola Gay minding how many men were on Iwo Jima when it flew to Japan. Just saying...

The over 'Effective Military Strength' and 'Galactic Battle Readiness' is really more of a way for the player to gauge how well they are doing. Honestly, trying to change the 50% Battle Readiness only changes a few lines in the game, and has no other significant impact (and if you didn't know how to change that, play the multiplayer on-line). I'm not sure how much you need for the Combat/Support strength ratings to get the endings you want, but you can skip out on a few easily without any real detriment. All those people worth 25 or 30 points (like, um, scientists, former allies, and seriously the Destiny Ascension, touted to be the most powerful of the Dreadnaughts, and is just as effective as Jacob Taylor?). Some decisions and efforts don't go to waste; the Leviathan Corp is worth 400, and most of Hackett's Dirty Laundry Runs usually gain you about 100-150 for your troubles. You honestly get decent points on recruitments; telling the little arguing folks to support the war effort, or join to go shoot somebody, more so than planet-scanning in some cases.

It makes no logical sense that a deathray machine that would make Darth Vader proud would give you such different results over minor changes. It would make more sense that say snagging certain allies and scientists would change the outcome. Having Rachni drones on the Crucible makes much more sense for a more positive outcome as oppose to... Strike Team Theta. I liked the Quarian/Geth issue; choose one or the other, and choices made in a previous game gave you the best of both worlds option. I wish that BioWare had done that more. Killing off the Counsel in the first game gave the Turians more ships supposedly, but you wouldn't notice it. Too many decisions and choices didn't seem to have affect whatsoever, or just a little bump on your galactic readiness. Concept was great, but delivery not so much.

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