This is why I believe skills should atrophy at a certain rate if you don't use them for a long period of time. Successful writer and researcher Malcolm Gladwell claimed that, as a rule of thumb, it takes roughly 10 000 hours of hard practice at something to truly master it. This is why having a character with 100 in every skill doesn't make a lot of sense. You would have to be some sort of God living for thousands of years to accumulate that degree of expertise in every single skill field, right?
Of course, someone fairly adept in a field with some years of experience won't degrade too much after a few months or even years neglect, and that is why there should be thresholds. My friend, who used to be a guitar wizard, stopped playing for about 2 years. He recently picked up the guitar again and, as expected, was nowhere near where he once was. But less than a week later he was back up to speed, scorching the fretboard with his shredding. Thus, there should be certain thresholds that, once you pass in skill level, your skill cannot degrade below. For example, if the threshold goes in increments of 20, ie 20, 40, 60, 80, etc., then if you were to get your lockpicking skill up to 44 and do not use it for a long while, the lowest it will degrade to would be 40, because you remember the basics of all you knew before. You could then easily get it back up to 44, and beyond if you keep training it. I used increments of 20 just as an example here. A better model would probably be increments that start of large, and exponentially decrease. For example the thresholds could proceed as 20, 40, 50, 60, 70, 75, 80, 84, 88, 90, 92, 94, 96, 97, 98, 99...ad infinitum - this will mean that you will have to almost constantly be training up in the higher levels to stay at your cutting edge peak, which is how it is in the real world. Also I do not believe there should be a hard cap, as there is no 100 "perfection" level that any human can obtain at a skill.
I believe mechanics like this would be interesting to have modeled in the game, and would create a dynamic forcing the player to think a bit more about which skills they use or how often. In order for this to be effective, it is obvious the rate of atrophying would not have to be non-linear, hence the term "learning curve". The rate of atrophying might be fairly high early on in low skill levels, and would taper off as it gets higher. This makes sense because you are using skills a lot early on anyway, and this would further define your characters proficiencies. I think this would be a cool addition to the game, and will mod it in if it's not in vanilla (which it probably won't). What do you guys think?