Almost nobody gets injured by one bad session. They get injured by a pattern that was visible for three weeks and that nobody was paid to point at.
Hard sessions while ill, or just after
This is the biggest one, and the easiest to avoid. Training hard with a fever, or in the first days after a bug, is how a week off becomes a month. If you have been ill, easy is the whole plan until the symptoms and the numbers agree.
Too many big days in a row
A big day is one well above your usual. Two in a row is a choice. Three or four is a pattern, and it is the shape of most overuse injuries. The fix is boring: put something easy between them.
Run distance that jumped
Running is where the body complains first, because every step lands on the same structures. A week that is far above the one before it, in running, is worth a flag whatever the plan says. Hold the next week back and keep the long run easy.
Strength that never happens
Two sessions a week is not glamorous and prevents more injuries than any foam roller. If you have had one in a fortnight, that is worth a nudge, and a short session is better than a perfect one.
And the race-specific gaps
Open water swimming before an open water race. A long ride before the saddle sores arrive. Riding outdoors if the race is outdoors, so handling and gearing are not a surprise. A brick, so your legs have met a run off the bike. None of it is dramatic. All of it is much cheaper in September than on race morning.
Shown three at a time, ranked by how much each matters, and snoozed when you say you have got it. That is the idea behind LankFit's watch-outs.