Reminds me of when I first found the value of a tire gauge, had recently gone back to a road style bike, having not ridden my Schwinn Super Sport for many years at that point, but having had a new fangled mountain bike for a coupla years. I had always just used my fingers....fairly firm on the mountain bike and really firm on the skinny tires
. Went on a ride that had too much crappy asphalt and kept flatting from pinch flats....with a couple spare tubes and a repair kit I still barely avoided walking the last bit home (and I probably just squeezed the tires after the bike had been sitting a few days or a week before I went out on the ride). In reading up learned about pinch flats and the importance of proper tire pressure, particularly with my 700c wheels with 23mm tires (being all racer boy minded, much narrower than my old Schwinn used even tho similar diameter)....so I used my pump with gauge back home and figured out my fingers were useless at higher pressures (since my portable frame pump had no gauge), I was consistently underinflating them judging them that way. Now it's somewhat the other end of the spectrum with my 27.5" fat tires....where like you say a psi or two does make a significant difference and my fingers are just lousy at it. I have a few gauges now for home and on the road/trail.