I'm an accountant and I have a number of self made millionaires as clients and I have a few observations.
When you have no money, you fantasise about having loads for the ease of life it provides. Totally get that.
Once you have got money, you don't want to lose it. So you want to put it somewhere safe. Even putting it somewhere risky-ish doesn't give great returns, especially as, if you're fairly young you have to think about inflation - ie you can't really put £1m in the bank and expect to live a good life off the £40k (4%) interest forever. £40k won't be worth too much in 20 years.
So you have this pot of money, which is great. But you don't want to spend it, don't want to lose it, and it's likely not the final solution to all things money as inflation is knawing away at it.
So you have all that worry and realisation that the couple of million you made isn't as good as you imagined. Plus, because your a millionaire now, you bought a nice house and want a nice car so your bills have gone up. So the investment returns on what you invest definitely isn't going to cut it.
Ultimately, you carry on hunting for some way of bringing money in. Such as work of some sort. It can bring in a decent amount vs interest/rent or whatever, and it can increase by inflation (at least to some degree) and it saves depleting your cash pile at a youngish age (anything pre 50s young from this POV).
All in, those I know who have made a few mil are not retired and chilling out living on the investment returns. They are still doing some kind of work and have decisions and worries and work in relation to the cash pile they have (or whatever assets they have put it into).
Sure, it is way better than having no money, but a few mil isn't quite as magical as many people imagine. Just my perspective, anyway.