Of all the millions mysteries or questions which are going to be left unresolved or open to interpretation there has been two between season 5 and 6 which I have never been able to explain myself. One is why the losties time travelled back to 1977 when they went back to the island in the Ajira and why they return to present in the Incident. I think a plausible explanation for the second is what has been discussed by LostinCanada and Shawn4168 in relation to course correction, in resume what happened in The Incident with Jughead was just this:
"That is what happens when anyone attempts to break the rules of time travel. They tried to change the past and the rules of time travel avoided the violation of the inalterableness of the past."
Any suggestion to why travelled to 1977 when they were on board of Ajira? It has been suggested that because they were supposed to be there to detonate (or not) Jughead in the Incident, something which always happened in the reality we know as the OT but that's not possible as The incident is the effect caused by the initial time travel. Any thoughts? Time Paradoxes, midiclorians or mystical explanations are welcome :)