Why do people always pop up on threads like this and say "Well I have <whatever condition> and I work a sixty hour week, because I have to, and you just get on with it don't you, and yes my legs fall off and have to be reattached sometimes but that's just life when you've got a mortgage to pay, I've never asked anyone else for a handout, work is essential for self-esteem and we have a problem with entitled attitudes and generational worklessness, people wouldn't be laying about claiming [a benefit that has nothing to do with whether you work] if they weren't getting all this money out of my taxes, what would they have done in Victorian times, etc. etc. etc.…"
Firstly, if they really have it that bad, maybe they should be claiming PIP themselves. If they're not eligible, then their situation isn't comparable to that of someone who is eligible.
Secondly (and this is an almost embarrassingly simple concept, but one which seems to elude many such commenters), medical conditions are not like mass-produced bricks. They're not all churned out on a production line and interchangeable with each other.
For one person, their eczema may mean a recurrent dry itchy patch on the back of their hands in winter. For another, their eczema may be an extremely painful, unbearably itchy, extremely conspicuous disability that heavily restricts their movement and activities, and requires a great deal of time spent on management of the condition.
For one person, their depression may mean they spend a couple of months feeling really quite low, every few years or so, and they need to make sure they get out for some brisk walks and spend time with friends to help themselves rediscover joy in their lives and recover. For another, their depression may mean they're so mentally slowed, heavy and achy that they can barely speak or move, they feel no emotions but a yawning, agonising blankness, they can't marshall their thoughts sufficiently to plan a trip from bed to toilet and back, they see sinister hallucinations of evil around them, they go unwashed for months on end, and they stop eating and drinking and need to be admitted to hospital to save their lives.
I feel almost like I'm pointing out that sky is up and ground is down, but it apparently needs saying: different people with the same condition may have a different manifestation of that condition.
Even when two people have similar manifestations of the same condition, people's situations and personal characteristics may affect how they cope with it.
And people with multiple conditions may find they interact with each other in ways that multiply the difficulties. To pick a couple of conditions almost at random: Many people do just fine and hold down jobs while experiencing mental health problems. Many people do just fine and hold down jobs with coeliac disease. But say you were a coeliac and also had mental health problems, and these mental health problems affected your ability to follow the gluten-free diet. You'd likely get gut symptoms, deficiency symptoms and long-term damage. And the symptoms you experienced might affect your ability to participate in daily life in a way that would help your mental health problem. The interaction between the ways your conditions affect you causes an extra problem. And no amount of people saying "I'm coeliac and I manage fine" or "I have mental health problems and I just have to get on with it" or even "I have mental health problems and coeliac disease but I still manage to stick to my gluten free diet" is going to help, because those people don't have the same experience.