In the last couple of weeks I've seen multiple riders going up hills in gears so tall that their pedals were barely moving.
In one case it was two heavy-set women, being a heavy-set man I'm not being critical of this - merely setting the scene. They were straining, really straining, to get up a long incline that was around a 5% grade. Both were riding multi-geared bikes. From the rotation of their pedals, I'd say they were at least two gears too tall. I felt like yelling, "Shift, Shift!!"
Then today, in 90+ degree heat, I saw a man, slightly heavy-set, working his way up a slight incline of about 2%, and just barely keeping his pedals moving. It made my knees hurt to watch him.
It makes me wonder why people make it so hard on themselves. If someone is able to power up an incline in a tall gear at an impressive rate of speed, then more power to them. I admire that ability. But when someone is barely moving and is red in the face from the effort to force the pedals down, and they have several lower gears available, why don't they try using them? Especially when they aren't in the greatest physical condition.
Two of the three had their seats too low too, which doesn't make going uphill any easier.
One of the biggest reasons I've been able to ride more miles is that I've learned, from reading posts here and from riding with a friend, is to spin one's way up inclines. This has been a great thing to learn.