Does heart rate always match how hard a workout feels?

Something I’ve noticed is that the number on the screen and the actual effort don’t always seem to match. There are days when a workout feels harder than expected even though the heart rate isn’t particularly high, and other days when the number is higher but the session feels fairly manageable.

I have HeartShare set up with an HR sensor for keeping the reading visible, but I’m more interested in understanding the difference between the number and how the workout actually feels.

Has anyone else noticed this? What do you normally trust more when the heart rate and perceived effort don’t agree?