WARNING: Large spoilers for the last few episodes of Fringe.
At the end of "The Boy Must Live", Michael allows himself to be captured by the Observers by stepping off a monorail just as it's leaving the station.
Later, in "An Enemy of Fate", Olivia and September have this conversation:
OLIVIA: Why would he step off the monorail? I mean, why would he do that? He knows too much. He must have known that they wanted to harm him.
SEPTEMBER: Apparently... there was a reason. There always is.
So far as I can tell, this never comes up again. The consequences of Michael's action are:
- Olivia making a last trip to the Other Side in order to get him back
- Broyles getting captured by Windmark, and as a result
- The Fringe team having to execute the plan under time pressure instead of at their leisure.
Once the plan is executed, time resets anyway, so it doesn't much matter how it happened.
Is there any indication given in the show of what Michael's reason for getting captured was? Which of those consequences were necessary in order for things to work out properly, or is there some other one that I'm missing?