Of course, but life doesn't always work out how you planned, job markets change, needs change, situations change. Unforseen circumstances can derail the best laid plans. People can take financial advice (remember endowment mortgages?) that turns out to be catastrophic, etc.
Yes, planning gives you a better chance, but the best laid plans are subject to change. I see a lot of people on MN, for example, smugly claiming they have saved for their old age. Most people have no idea just how much nursing care can cost. My parents have worked, saved and invested. Done all the right things, have a comfortable retirement, but if one of them needs care before the other, so they can't sell their home as one needs to live in it, all their carefully built up savings will last about a year. Their hard-earned company pensions don't add up to the £1,500 a week that it would cost for residential care plus the living costs of the one left at home. Hopefully, this won't be the situation, but if it happened, yes, they'd need state intervention. I will likely step in and look after them myself if I am physically ably, but that will affect my income and my carefully laid plans. I have just seen this exact scenario play out with close relatives, all of whom had plans, savings, investments.
The vast majority of people who have worked, saved and invested won't have double-income six figure salaries. Not because they have been idle, or haven't planned, but because most jobs aren't in the top earning percentage. They just aren't. And the truth is, unless you really are in one of the few professions that put you at senior level wages, you won't have enough money to support more than a year or two in a nursing home, paying for yourself. Some people can live for years needing 24 hour care.