I agree and disagree with what's been said so far. To me a frog is not a pet to be petted. You don't walk them on a leash, you don't go jogging with them, they don't fetch. They are to be quietly (or in the case of male WTFs not so quietly!) admired, in their tank or on your gloved hand at their own comfort. If a frog does not want to spend time sitting on you than don't force him to, leave him in his cage where he is relaxed and stress free. Now, that being said, in the interest of necessity when it comes to medicating or treating frogs for injuries or illness, I believe LESS stress will,be caused if they are already well familiar with being picked up and gently and calmly examined-- not stroked, not petted or patted or tickled-- examined. Some things simply cannot be seen with the frog in its enclosure, and for some methods of treatment same idea. I also want my frogs to be used to being placed in different containers, whether a small hospital tank, or a carrier in case they need a trip to the vet, or when we finally are able to move. If for some reason they need to be switched into a different setting I don't want them freaking out and causing themselves damage. Also, what if there is an emergency and you need to move your frogs FAST, a frog that has learned there is nothing to fear from being picked up and held will be easier to evacuate.
I personally believe that frogs (some frogs anyway) are intelligent in their own way, and certain species can be amiable to interacting with humans, albeit in a minimalistic way. When I was growing up we kept a collection of various PCFs for years (our oldest was 8-years-old). Some of these frogs showed, what was to me at any rate, obvious smarts and were clearly at ease with their people. Junior, the PCF we had the longest, would crawl out of his tank onto my mother's hand and hitch a ride to the dining room table. Back then we had no idea of feeder insects for sale (this was years ago) so, aside from giving wild caught bugs, she fed them a homemade mixture of lean hamburger mixed with fish vegetable flakes and conditioning food. She would ball up a fly size portion, and using a flat ended toothpick, would pry open the frog's mouths, pop in the food, and gently stroke their gullet with the flat side of the toothpick until they swallowed. Now, some of the frogs always had to be fed this way, but not Junior (or Cousin, Gwendolyn, or Green Girl). Junior would sit on the table, the top of the jar we used to transport the other frogs from tank to table, or just on the table, watching all the goings on. I don't remember when he first got it into his head to try grabbing the food on his own, but the day he did he never had to be force fed again. He would wait for mom to hand him his bite of food and he'd take it right off her finger. Junior would sit on my mom's hand while she dialed the phone (rotary mind you) and when she sat down to talk he'd climb on the funny "vine". We always washed our hands well before and after handling the frogs, and we didn't "handle handle them", they climbed on us, we didn't grasp them or hold them in closed hands, unless it was for a moment to transfer from jar to tank. If they didn't like to interact with us we only handled them enough to get things done, we never forced it on them. But Junior was different, he was a very special frog and I'd say unusual. He lived a long time for a PCF and died of old age, healthy and never having had any injury, illness or disease. The same unfortunately can't be said for many frogs coming out of pet shops today.
All that being said, I'm very glad that I know more about frog feeding in particular these days... I would never feed raw hamburger to a frog now-- I won't even eat beef burgers! And there's been great advances as far as supplement powders, a wide variety of farm raised feeder insects, water conditioners, and etc. goes. The environment isn't what it was when I was a kid, and it still needed improvement. Anyone remember the commercial against pollution that featured the Native American Indian man (Iron Eyes Cody) in the canoe, and how all the trash and polluted streams and waterways made him cry?

I will never forget that commercial... it's just too bad that no one back then seemed to have learned a darn thing. Frogs in the wild are becoming extinct at an alarming rate now, back then we never imagined such a thing happening. Or at least I didn't. I just want to do the best for my frogs that I can.
Here's the commercial, found it!
https://www.youtube.com/watch?v=KF-U0dL-9K4