When I was maybe 15, my mother had a friend who had in previous years made a very good income as a day-trader. He was very well off. He quit doing that and got a regular job because successful day-trading required so much work, analyzing and tracking and watching everything so closely that he had no time for anything else. When he married, he wanted to have time for his new family.
I don't think you're seriously considering a shift from "invest a few bucks to be part of something you believe in" to "day trading".
Diversification is really important to you, as is avoiding risk. Have you stopped being diversified by being invested in mutual funds, index funds, etc...? My impression is that your TSLA investment hasn't changed - a few bucks early on to be part of something. The fact that it's grown to be a big number doesn't change the size of your original investment, or your reason for the investment?
So yes, it's a big number. But does that matter?
Falling like a rock. From a peak of just over $500 it's now under $400. That's a 20% drop!!! Wish I'd sold some at $500. Of course I'll change my mind if it goes back up and breaks $500 again. This has always been an extremely volatile stock. I need to just stop looking at it!
This observation looks like to me like something that comes out of a "time the market" mind set. My own view of a long term buy and hold, or buy a few shares to be part of something you believe in, is that the price at any moment in time is irrelevant (unless the total position can / does change your life in a vector that is important to you).
Rather than "time the market", the question I would ask is:
1) has your original intent when you bought some TSLA changed?
2) has the value of the position increased enough to change your life?
if either answer is yes, then the time to sell is now. Let it go and enjoy the rewards of your investment, or let it go because what you believed in back then has changed and/or you know longer believe that TSLA satisfies your original intent (buy a few shares to be a part of something you want to be a part of).
Either way, the price today doesn't matter - the reason you got in has been realized.
The way I look at it, as a long term buy and hold investor, the share price doesn't matter (until it changes your life). What matters is whether the company is still doing what you invested in. The moment it stops satisfying your investment criteria, then you're out. The price at that moment doesn't matter - you're now invested in something you don't believe in. It really is that simple (for me at least! your mileage may vary).
My guess is that you're still getting what you were looking for when you put a few bucks in (be a part of something you believe in). So sit back and enjoy the ride - whether there's a few more 0's on the end of your original investment, it's still the original investment and the original purpose is still there. And you're still diversified, so the amount of money on the line hasn't changed.
And someday (which could be today), maybe the amount of your 'be part of something' investment is enough that it moves the needle on your financial life (woot!) and it's time to sell and enjoy that outcome.