my body just told me off in real time

So I've been doing legs every Tuesday for like two months now and I thought I had it figured out. Same machines, same weights, same order. Felt comfortable. Today I jumped straight into squats — like straight straight, barely moved for two minutes beforehand — because I was running late and honestly just wanted to get in and out. Third rep and my left knee just went... not painful, more like a warning. That weird tight feeling where your body's basically going "excuse me what are you doing." Had to step back, do a proper warm-up anyway, and by the time I actually started working I was already ten minutes behind where I thought I'd be. So I saved no time. At all. I genuinely outsmarted myself there. The annoying thing is I know this. I've been told, I've read it, someone in this community mentioned it ages ago. It just doesn't click until it happens to you does it. My hips especially — I've noticed if I don't do at least some hip circles and slow bodyweight squats before loading anything, the whole session just feels off and stiff the entire way through. Doesn't matter how warmed up I feel from walking to the gym. Four months in and I'm still learning the same basic lessons lol. To be fair though, knee felt fine after the warm-up and I actually had a decent session so — small win I suppose.