so, how does breaking a time loop cause a doomed timeline to happen?

Okay, imagine this. Outside of the Alpha, outside of larger, grander loops. Imagine that you’re a Time Player, and during a fight with an Ogre, you get knocked down a cliff. At the very bottom there’s spikes facing upwards, and you have no means to save yourself from that fall. However at the last second, a Time-Travelling Future Self appears on a jetpack, and saves your ass.

Now, knowing this, you have two options. If you eventually make a Jetpack, and go back in Time to save yourself, then congratulations! You’ve complied with the rules set by your Time Travelling, closed a Time Loop, and ensured continuity will keep going as expected.

Your other option is to actively avoid doing this. You never make a jetpack, you never Time Travel back to save yourself, you never close this loop. As such, your actions are leading towards a reality where you never actually went back in Time to save yourself! As such, you never saved yourself- Which means you create a paradox, and you should not exist in the first place because you should be dead. However, you DID get saved by yourself, that is an immutable fact!

A Time Loop is retroactive. You were saved by yourself, so you eventually have to go back to save yourself. Because you’ve already seen it. It has happened. The true, Alpha Reality is that it has happened. And if you deviate from it, you’re branching away from the Reality you saw. As such, you are Doomed. Doomed by your own choice, to be an offshot version, and marked for Death by Paradox Space.

Note, however, that there’s a lot of nuance involved with Time Travel- The Alpha Timeline is, at its core, a huge Time Loop that spans the entire adventure, that you cannot break off from without dying. So sometimes, its effects will appear to be the OPPOSITE of what I described! Like the first Dead Dave. He went back in time to stop DD- But ended up dying. Dave NEEDS to be alive in the Alpha Timeline, and DD needs to take the code to create Becquerel in the Alpha Timeline. As such, a Timeline in which Dave goes back and kills DD cannot be the Alpha, because Becquerel won’t be created. And a Timeline where DD kills Dave cannot be the Alpha, because Dave needs to be alive. As such, the moment Dave decides to go back in time, that ‘Dave’ becomes a Doomed Iteration, and dies- Which is what then makes Alpha Dave NOT Time Travel, and as such keeps complying with the Alpha Timeline’s will.

Davesprite is similar, he prototyped Lil Cal, breaking the entire chain of events that would come next. Knowing this, John lets Typheus kill him so Dave and Rose know they’re Doomed and try to fix it, and Dave goes back in time to become Davesprite. The deviation from the Timeline caused a Doomed Timeline, and correcting it rails causality back along the Alpha Timeline, the sequence of events that Must Happen. As such always have in mind that, while Doomed Versions are slated for death, marked to be taken down, their presence in the Alpha Timeline is often used as the deterrent factor that ensures the Alpha Timeline.

A lot of times, the ‘Alpha Timeline’ is, because Doomed Realities that happened were unfavorable, and the Time Player tried to change them. And while a big chunk of it is decided by Lord English, smaller Time Loops and corrections can be created by everyone, with every choice they take. And in the same way, a simple choice of choosing ‘heads or tails’ could determine if you are the Dave that Lives, or the Doomed Dave whose throat is about to be sliced open by Bec Noir.