Back in the day, as a distance runner, I occasionally pushed certain weeks a bit beyond my overall endurance and/or nutrition at that point in the season. Not often, but occasionally. I never viewed that as over-training on the larger scale, but rather as a short-term misjudgment of my stamina. Sometimes, it was lack of electrolytes. Sometimes, the distance was at the limits of fueling. Occasionally, I'd gotten back from an illness or downtime with insufficient stretching or prep for the effort. But, nothing long-term, thankfully.
My big take-away then, as now: listen to the body, because it generally knows. There are all sorts of feedback signals the body will send to ensure we know we're at the limits. If we're listening, and adjust accordingly, we can generally pull back from the edge easily.
Have never pushed hard enough in cycling, over time, to come near those limits. Uh, other than that one day, doing the better part of a century with an aspiring racer who showed me what a hard pace could be. Couldn't walk, run or ride properly for several days, after that. But that was a one-time deal, that hard.