How reliable is "promised" shipping time, really?

[Wild.cats]

How often do carriers actually hit the shipping time they promise? I'm not talking about general estimates, but those specific 2-day or guaranteed by Friday types cos lately I've noticed a few packages showing up a day or two late, even when everything looks smooth on tracking. No weather delays, no holidays, just... late and it just makes me doubt whether the shipping time is as they promise, or if it's more of a marketing thing than a real commitment.
Is this just how it is now, or are some carriers still mostly on point?

 

[gary09]

I’ve noticed the same lately those guaranteed delivery windows don’t always hold up. Even without delays showing some carriers still miss the mark. Feels like its more marketing than a true guarantee now. UPS and FedEx used to be solid but even they slip sometimes. Best to track closely and always check the fine print I think

 

[Banbyy]

I totally get your concern, it's frustrating when you plan around a guaranteed delivery and it still shows up late, it makes you wonder if you can even trust those promises anymore

 

[TransitTitan]

Absolutely, you both make a good point. I've noticed those "guaranteed" windows slipping a lot lately as well, even when everything seems to be in order. It feels more like a marketing phrase than a solid guarantee these days. Have you come across any carriers that are still reliably consistent for you?