The first thing the time travelers learnt was that it is very to mess up and destroy your timeline. Not in the way most commonly depicted in fiction, where the protagonists return to the present only to discover that the circumstances under which they and they families live have altered dramatically (a concession to the real-world fact that fictional time travel is a great excuse to put actors in new costumes), but in the slightly more brutal way of you and everyone you’ve ever known have been preemptively eliminated from history. It is a specific kind of bummer to find that the new timeline caused by your interference does not (and never will) include you in any way whatsoever
This lesson was learnt by messing up the timeline, and then having said messing of up prevented by someone from an upcoming timeline interfering and stopping it outright. It was hinted that this interloper arrived from a place hundreds of timeline alterations upstreams, but alas, we will never know for sure, no matter how many times we ask
The second thing the time travelers learnt was that timelines are strangely robust when it comes to alterations of routine events with high probabilities. An extra face at a large sporting event makes no difference to or fro. The same goes for any kind of large scale social gathering with a semblance of anonymity – as long as the travelers are part of the crowd and only intervenes in ways heavily scripted by the social situation, their impact is negligible to nonexistent. If something was likely to happen at one particular such gathering, it would happen the next time, had it been prevented somehow
Thus it came to pass that one of the main uses of time travel was to gather contextual information about already known events. In particular, literary scholars sent themselves back in time to attend university lectures and seminars on important (and contemporary) works of fiction. Ironically, authorial intent is a lively business
More longer friend see that sky? 