My wife always reminds me to ‘not go too hard’. Sure, not every ride should be hard. But when it’s ‘game on’, my limit is whatever my body will physically let me get away with. I can go pretty long under my threshold HR (about 163), limited time above 170-ish) an only short hard efforts at MHR.
I also train with power, and can use that to self-regulate my efforts as to keep me from going too deep into the red on either climbs or hard pulls. Whenever I burn a match, I absolutely must recover from that, which usually translates into getting dropped.
Finally,
I (try to) use polarization training (easy days easy, hard days hard) to be fresh when it’s needed. Otherwise, I’ll be fatigued and utterly worthless on my bike.