My 58-year-old father put his entire 401k into Tesla stock. How do you explain the volatility risk and lack of diversification to a parent?

I've been stressed about my father's retirement savings ever since he told me he converted his entire savings from a normal target date fund to 100% Tesla stock. This occurred in 2020 around the same timeframe of the first stock split, and all contributions to date have been Tesla.

For background both my dad and I have loved the company and their products for years, but we differ in that I think the stock is heavily overpriced, and he has latched on to the valuations and extremely bullish forecasts people like Kathy Woods assign to Tesla. He's convinced the stock is going to rocket to 4 - 10X its current value before he retires, and hasn't really reacted to the bearish arguments I've laid out acknowledging how much more expensive the company is than every other automaker and how competition is increasing in the space. Not to mention that much of its valuation is currently highly speculative such as "robo-taxis" while their FSD is starting to fall behind competitors in execution and is still not (and may never be) fully delivered.

Setting the valuation of Tesla debate aside, I would never advise any person at any age to put 100% of their retirement portfolio in any single stock, let alone one as risky as Tesla. I've tried explaining the extreme risk in a zero diversity portfolio, where if this single company goes under he loses his entire retirement fund ("all your eggs are in one basket"), but he doesn't seem to take it seriously.

My fear is that he is already behind on where he probably should be in his retirement savings. He's told me before he spoke with a financial advisor before doing this, and he didn't have enough funds to manage with them. I feel he is making this gamble as he thinks its the only way to catch up, not recognizing he could also lose it all. I know he has not talked to any advisors since about his current investment strategy.

Some questions I'm hoping you can help answer for him and I, so he has an outside perspective:

If you are neutral or bearish on Tesla, how would you explain the issues and risks with its va;ue going forward?

If you are bullish on Tesla, are you investing 100% of your savings in it, and would you advise a 58-year-old to do the same with their retirement savings? Why or why not?

How would you explain the risk of his current plan to him, and what alternatives would you suggest?

What should an ideal retirement portfolio look like for someone his age?

What resources do you believe would be good to share with him that might help reopen the conversation on reducing his risk and impressing the importance of diversification?

It's not an easy conversation to have with a parent, and ultimately I respect that he's an adult who can do what he wants with his money. I've tried a few times to have it but its difficult to balance not being taken as condescending to your own father while explaining how insanely risky you think his financial decisions are. It's made it more difficult by the high upturns TSLA has taken in stretches, validating all his beliefs, but with the subsequent downturns he's doubled down and not acknowledged the volatility and risk. I fear with him consuming positive bullish Tesla content exclusively, he is not considering bearish outcomes or basic retirement savings advice. Any feedback from the community that can offer an alternative view would be highly appreciated, as I hope I can share some of your resources and opinions with him next time I retry this conversation.

Thanks so much!